Students can access the CBSE Sample Papers for Class 10 Science with Solutions and marking scheme Set 4 will help students in understanding the difficulty level of the exam.
CBSE Sample Papers for Class 10 Science Set 4 with Solutions
Time Allowed: 3 hours
Maximum Marks: 80
General Instructions:
- This question paper consists of 39 questions in 5 sections.
- All questions are compulsory. However, an internal choice is provided in some questions. A student is expected to attempt only one of these questions.
- Section A consists of 20 Objective type questions carrying 1 mark each.
- Section B consists of 6 Very Short questions carrying 02 marks each. Answers to these questions should be in the range of 30 to 50 words.
- Section C consists of 7 Short Answer type questions carrying 03 marks each. Answers to these questions should be in the range of 50 to 80 words.
- Section D consists of 3 Long Answer type questions carrying 05 marks each. Answers to these questions should be in the range of 80 to 120 words.
- Section E consists of 3 source-based/case-based units of assessment of 04 marks each with sub-parts.
Section – A (20 Marks)
Select and write the most appropriate option out of the four options given for each of the questions 1 – 20. There is no negative mark for incorrect response.
Question 1.
Identify the correct option from the given table which represents the type of reactions occurring in step 1 and step 2.
Option | Endothermic | Exothermic |
(A) | ✘ | ✔ |
(B) | ✔ | ✘ |
(C) | ✔ | ✔ |
(D) | ✘ | ✘ |
Answer:
(C) | ✔ | ✔ |
Explanation: When limestone is heated, it absorbs heat (endothermic) and decomposes to form calcium oxide. When water is added to this calcium oxide (lime), calcium hydroxide, Ca(OH)2, ie., slaked lime is formed. This is an exothermic reaction.
Question 2.
Which one of the following properties is not generally exhibited by ionic compounds?
(A) Solubility in water.
(B) Electrical conductivity in solid state.
(C) High melting and boiling points.
(D) Electrical conductivity in molten state.
Answer:
(B) Electrical conductivity in solid state.
Explanation: lonic compounds in the solid state do not conduct electricity because the movement of ions in the solid is not possible due to their rigid structure.
Question 3.
Ethane, with the molecular formula C2H4 has:
(A) 6 covalent bonds
(B) 7 covalent bonds
(C) 8 covalent bonds
(D) 9 covalent bonds
Answer:
(B) 7 covalent bonds
Explanation: Ethane has 7 covalent bonds. One bond is between two carbon atoms and the rest of the six is between hydrogen atoms.
Question 4.
When sodium bicarbonate reacts with dilute hydrochloric acid, the gas evolved is:
(A) Hydrogen; it gives a pop sound with burning match stick.
(B) Hydrogen; it turns lime water milky.
(C) Carbon dioxide; it turns lime water milky.
(D) Carbon dioxide; it blows off a burning match stick with a pop sound.
Answer:
(C) Carbon dioxide; it turns lime water milky.
Explanation: When sodium hydrogen carbonate (sodium bicarbonate) is treated with dil. hydrochloric acid, a brisk effervescence is observed.
This is due to the release of carbon dioxide gas.
NaHCO3 (s) + HCl (aq) → NaCl (aq) + H2O (l) + CO2 (g)
When carbon dioxide reacts with lime water, lime water turns milky due to the formation of calcium carbonate.
Ca(OH)2 (aq) + CO2 → CaCO3 (s) + H2O (l)
Question 5.
When aqueous solutions of potassium iodide and lead nitrate are mixed, an insoluble substance separates out.
The chemical equation for the reaction involved is:
(A) KI + PbNO3 → PbI + KNO3
(B) 2KI + Pb(NO2)2 → PbI2 + 2KNO3
(C) KI + Pb(NO2)2 → PbI + KNO3
(D) KI + PbNO3 → PbI2 + KNO3
Answer:
(B) 2KI + Pb(NO2)2 → PbI2 + 2KNO3
Explanation: When an aqueous solution of potassium iodine and lead nitrate is mixed, an insoluble yellowish lead iodide is formed along with potassium nitrate.
The chemical reaction involved is:
Pb(NO3)2 + 2KI → PbI2 + 2KNO3
Question 6.
Identify the basic salt from the following salts:
(A) Na2CO3
(B) NH4Cl
(C) NaNO3
(D) KCl
Answer:
(A) Na2CO3
Explanation: Na2CO3 is a basic salt. It is made up of a strong base (NaOH – sodium hydroxide) and weak acid (H2CO3 – carbonic acid).
Question 7.
Bronze is an alloy of:
(A) copper and zinc
(B) aluminium and tin
(C) copper, tin and zinc
(D) copper and tin
Answer:
(D) copper and tin
Explanation: Bronze is an alloy of copper and tin.
Question 8.
Stomata are the tiny, kidney, or bean-shaped pores or openings present in the epidermis of the cell. Opening and closing of stomata is due to:
(A) high pressure of gases inside the cells.
(B) movement of water in and out of the guard cells.
(C) stimulus of light in the guard cells.
(D) diffusion of CO2 in and out of the guard cells.
Answer:
(B) movement of water in and out of the guard cells.
Explanation: The opening and closing of the stomatal pore is the function of guard cells. They swell when water flows into them, causing the stomatal pore to open and on the loss of turgidity the guard cells become flaccid leading to the closure of the stomatal pore.
Question 9.
Adolescence is a unique stage of human development and an important time for laying the foundations of good health. During adolescence, the reproductive phase starts and:
(A) general growth rate begins to slow down.
(B) height becomes less.
(C) the body weight is reduced.
(D) hair growth decreases.
Answer:
(C) the body weight is reduced.
Explanation: Sexual maturation of reproductive tissues is a necessary link for reproduction because of the need for germ-cells to participate in sexual reproduction. The body of the individual organism has to grow toits adult size, the rate of general body growth begins to slow down and reproductive tissues begin to mature during adolescence.
Question 10.
Which one of the given statements is incorrect?
(A) DNA has the complete information for a particular characteristic.
(B) DNA is the molecule responsible for the inheritance of characteristics from parents to offspring.
(C) Change in information will produce a different protein.
(D) Characteristics will remain the same even if protein changes.
Answer:
(D) Characteristics will remain the same even if protein changes.
Explanation: Changes in protein structure can cause changes in the characteristic of an organism, as proteins are the molecules responsible for carrying out various functions in the cell.
Question 11.
Water in the root enters due to:
(A) the function of the root to absorb water
(B) difference in the concentration of ions between the root and the soil.
(C) excess water present in the soil
(D) diffusion of water in the roots
Answer:
(B) difference in the concentration of ions between the root and the soil.
Explanation: Water in the root enters due to difference in the concentration of ions between the root and the soil.
Question 12.
Which pair of sex chromosomes will determine a male?
(A) XO
(B) XX
(C) XY
(D) YY
Answer:
(C) XY
Explanation: In humans, all eggs of female carry X chromosome while sperm may have X or Y chromosome. The sex of the child depends on the type of sperm that fuses with the egg. If the egg fuses with the sperm carrying X chromosome, it results in a girl (XX) and if it fuses with the sperm carrying Y chromosome, it results in a boy (XY).
Question 13.
To obtain a magnification of + 2 with a concave mirror of radius of curvature 60 cm, the object distance must be.
(A) -90cm.
(B) -45cm
(C) -30cm
(D) -15cm
Answer:
(D) -15cm
Explanation: Given: Concave mirror has a radius
of curvature = 60cm
So, Focal length = 60/2 = -30cm
‘ve is taken because the focus of the mirror is behind the pole.
Given: Magnification = 2
Also, v is image distance, u is object distance and f is focal length.
As magnification = -v/u
Hence on putting the values we get, -v/u = 2
v = -2u
Now, putting the value of v and f we get,
u = -15cm
Question 14.
The change in the focal length of an eye lens in human beings is caused by the action of:
(A) optic nerves
(B) ciliary muscles
(C) retina
(D) cornea
Answer:
(B) ciliary muscles
Explanation: The relaxation or contraction of ciliary muscles changes the curvature of the eye lens. The change in curvature of the eye lens changes the focal length of the eyes. Hence, the change in the focal length of an eye lens is caused by the action of ciliary muscles.
Question 15.
Study the given figure of a food web and identify the primary consumer in the food web:
(A) Mice and Bear :
(B) Rabbit and Cat
(C) Rabbit and Fox
(D) Mice and Rabbit
Answer:
(B) Rabbit and Cat
Explanation: Primary consumers make up the second trophic level. They are also called herbivores. They eat producers. In the given food web, mice and rabbit are primary consumers.
Question 16.
Select the mismatched pair in the following and correct it.
(A) Bio-magnification — Accumulation of chemicals at the successive trophic levels of a food chain.
(B) Ecosystem — Biotic components of the environment.
(C) Aquarium — A man-made ecosystem.
(D) Parasites — Organisms which obtain food from other living organisms.
Answer:
(D) Parasites — Organisms which obtain food from other living organisms.
Explanation: Both biotic and abiotic components of the environment constitute an ecosystem.
Question Nos. 17 to 20 consist of two statements – Assertion (A) and Reason (R). Answer these questions by selecting the appropriate option given below:
(A) Both A and R are true, and R is the correct explanation of A.
(B) Both A and R are true, and R is not the correct explanation of A.
(C) A is true but R is false.
(D) A is false but R is true.
Question 17.
Assertion (A): It is advised that while diluting an acid one should add water to acid and not acid to water keeping, the solution continuously stirred.
Reason (R): The process of dissolving an acid into water is highly exothermic.
Answer:
(D) A is false but R is true.
Explanation: We should add acid to water and not water to acid. It is highly exothermic and may cause burns. Hence, the assertion is false but the reason is true.
Question 18.
Assertion (A): In humans, if gene (B) is responsible for black eyes and gene (b) is responsible for brown eyes, then the colour of the eyes of the progeny having gene combination Bb, bb or BB will be black only.
Reason (R): The black colour of the eyes is a dominant trait.
Answer:
(D) A is false but R is true.
Explanation: In humans, if gene (B) is responsible for black eyes and gene (b) is responsible for brown eyes, then the colour of the eyes of the progeny having gene combination Bb and BB will be black only. The gene combination bb will be brown. It is because the black colour of the eyes is a dominant trait and the brown eye is a recessive trait.
Question 19.
Assertion (A): In Fleming’s Left-Hand rule, the direction of magnetic field, force and current are mutually perpendicular.
Reason (R): Fleming’s Left-Hand rule is applied to measure the induced current.
Answer:
(C) A is true but R is false.
Explanation: Fleming’s Left-Hand rule is used to find the direction of force in a current-carrying conductor in the presence of a magnetic field.
Question 20.
Assertion (A): The energy which passes to the herbivores does not come back to autotrophs.
Reason (R): The flow of energy in a food chain is unidirectional.
Answer:
(A) Both A and R are true, and R is the correct explanation of A.
Explanation: The flow of energy is unidirectional. The energy that is captured by the autotrophs does not revert to the Sun and the energy which Passes to the herbivores does not come back to autotrophs. As it moves progressively through the various trophic levels, it is no longer available to the previous level.
Section – B (12 Marks)
(Q. no. 21 to 26 are very short answer questions.)
Question 21.
A student took a small amount of copper oxide in a conical flask and added dilute hydrochloric acid to it with constant stirring. He observed a change in the colour of the solution.
(a) Write the name of the compound formed and its colour.
(b) Write a balanced chemical equation for the reaction involved.
Answer:
(a) The compound formed is copper(II) chloride or cupric chloride (CuCl2).
The colour of CuCl2 is blue-green.
(b) The balanced chemical equation is:
CuO (s) + 2HCl (aq) → CuCl (aq) + H2O (l)
Question 22.
Give the name of the enzyme present in the fluid in our mouth cavity.
State the gland which produces it. What would happen to the digestion process if this gland stops secreting this enzyme?
Answer:
- Ptyalin or salivary amylase is the starch hydrolysing enzyme secreted by salivary glands in human beings.
- Amylase is a digestive enzyme that acts on starch in food, breaking it down into smaller carbohydrate molecules. Without amylase, a person will be unable to digest starch and sugars in the mouth.
Question 23.
List two differences between the movement of leaves of a sensitive plant and the movement of a shoot towards light.
Answer:
The type of movement of leaves of the sensitive plant is known as a nastic movement. This type of movement does not depend on the direction of stimuli.
The movement of shoot towards light is known as a tropic movement. This movement depends on the direction of light. This type of movement is directional and promotes growth development.
OR
What happens at synapse between two neurons? State briefly.
Answer:
Transmission of nerve impulses between two neurons takes place through the synapse. At the end of the axon, the electrical impulse sets off the release of some chemicals called neurotransmitters. These chemicals cross the gap or synapse and start a similar electrical impulse in the dendrite of the next neuron.
Question 24.
Observe the following diagram and answer the questions that follow:
(a) Identify the defect of vision shown.
(b) List its two causes.
(c) Name the type of lens used for the correction of this defect.
Answer:
(a) Myopia, as the image is formed before the retina for far away objects.
(b) Possible causes are:
1. Elongation of eyeballs.
2. Excessive curvature of the eye lens. we
(c) Correction: Using a concave lens of suitable focal length.
Question 25.
As shown in the diagram an aluminium rod ‘AB’ is suspended horizontally between the two poles of a strong horseshoe magnet in such a way that the axis of the rod is horizontal and the direction of the magnetic field is vertically upward. The rod is connected in series with a battery and a key.
State giving reason:
(a) What is observed when a current is passed through the aluminium rod from end B to end A?
(b) What change is observed in a situation in which the axis of the rod ‘AB’ is moved and aligned parallel to the magnetic field and current is passed in the rod in the same direction?
Answer:
(a) It is observed that the rod is displaced towards the left as force is exerted on the current-carrying aluminium rod when it is placed in a magnetic field.
(b) No displacement will be observed as the rod will not experience any force because the angle between the magnetic field and the current-carrying conductor is zero.
OR
When is the force experienced by a current-carrying straight conductor placed in a uniform magnetic field:
(a) Maximum
(b) Minimum
Answer:
(a) The force experienced by a current-carrying straight conductor placed in a uniform magnetic field is maxinium when the conductor carrying current is perpendicular to the direction of a uniform magnetic field.
(b) The force experienced by a current-carrying straight conductor placed in a uniform magnetic field is minimum when the conductor-carrying current is parallel or anti-parallel to the direction of a uniform magnetic field.
Question 26.
(a) State the essential function performed by layer P at the higher levels of the atmosphere.
Answer:
The function of the ozone layer in the upper atmosphere is to prevent harmful ultraviolet (UV) rays from reaching the Earth’s surface, as these UV rays cause various types of diseases including skin cancer.
(b) Why was there a sharp drop in the amount of ozone in the atmosphere in 1980s?
Answer:
The amount of ozone in the atmosphere began to drop sharply in the 1980s. This decrease is due to synthetic chemicals like chlorofluorocarbons which are used as refrigerants and in fire extinguishers.
Section – C (21 Marks)
(Q.no. 27 to 33 are short answer questions.)
Question 27.
A substance X is used as a building material and is insoluble in water. When it reacts with dil. HCL it produces a gas which turns lime water milky.
(a) Write the chemical name and formula of ‘X’.
(b) Write chemical equations for the chemical reactions involved in the above statements.
Answer:
(a) Substance X is calcium carbonate.
Chemical formula: CaCO3
(b) In the reaction between calcium carbonate and dilute hydrochloric acid (HCI), calcium chloride (CaCl2), carbon dioxide (CO2) and water (H2O)
are produced.
CaCO3(s) + 2HCl(aq) → CaCl (aq) + H2O(l) + CO2(g)
The carbon dioxide evolved reacts with limewater (Ca(OH)2 to form calcium carbonate and water.
Ca(OH)2(s) + CO2(g) → CaCO3(s) + H2O(l)
The production of calcium carbonate is responsible for the milky white colour.
Question 28.
“Two different forms of carbon – diamond and graphite have different structures and very different physical properties even though their chemical properties are same.” Explain why.
Answer:
Diamond and graphite are allotropes of carbon. Allotropes are the different forms of the element having different physical properties. The element carbon occurs in various forms in nature with different physical properties but nearly same chemical properties. Diamond is a giant molecule of carbon atoms in which each carbon atom is bonded to four other carbon atoms forming a rigid three-dimensional structure, which is responsible for its hardness. Graphite crystal consists of a layer of carbon atoms in which each carbon atom is bonded to three other carbon atoms in the same plane giving a hexagonal array. Graphite structure is formed by hexagonal array being placed in layer one above the other.
OR
Shown below are the structural formulae of four carbon compounds.
(a) Two of these compounds are more likely to have similar chemical properties. Identify these two compounds. Give a reason for your answer.
(b) Identify which of these compounds are likely to have the same boiling point. Justify your answer.
Answer:
(a) Q and S
They have the same functional group.
(b) None of them.
They are all different chemical substances.
Question 29.
(a) How does Paramecium obtain its food?
Answer:
Paramecium takes its food at a specific spot by endocytosis. Food is moved to this spot by the movement of cilia which cover the entire surface of the cell.
(b) List the role of each of the following in our digestive system:
(i) Hydrochloric acid
(ii) Trypsin
(iii) Muscular walls of stomach
(iv) Salivary amylase
Answer:
(i) Hydrochloric acid: The hydrochloric acid creates an acidic medium which facilitates the action of enzyme pepsin and it also kills the germs in the food.
(ii) Trypsin: Trypsin helps in the digestion of proteins into smaller peptides.
(iii) Muscular wall of stomach: The muscular wall of the stomach help in mixing the food thoroughly with more digestive juices.
(iv) Salivary amylase: Saliva contains an enzyme called salivary enzyme which breaks down starch to give simple sugar.
Question 30.
Some plants like pea plants have tendrils which help them to climb up other plants. Explain how it is done. Name the plant hormone responsible for this movement.
Answer:
Tendrils are sensitive to touch. When they come in contact with any support, the part of the tendril in contact with the object does not grow as rapidly as the part of the tendril away from the object. This causes the tendril to circle around the object and thus cling to it.
Auxin is the hormone that promotes the growth of the tendril around the support as it is synthesized in the tip of the shoot and stimulates the growth of the cells on the opposite side which causes the coiling of the tendril around the support.
Question 31.
In the figure given below, a narrow beam of white light is shown to pass through a triangular glass prism. After passing through the prism, it produces a spectrum XY on the screen.
(a) Name the phenomenon.
(b) State the colours seen at X and Y.
(c) Why do different colours of white light bend at different angles through a prism?
Answer:
(a) The phenomenon is called dispersion,
(b) X; Violet, Y; Red
(c) Different colours of white light bend through different angles with respect to the incident beam of light due to difference in the speed of light of different wavelengths.
Question 32.
An electric motor rated 1100 W is connected to 220 V mains. Find:
(a) The current drawn from the mains.
(b) Electric energy consumed if the motor is used for 5 hours daily for 6 days.
(c) Total cost of energy consumed if the rate of one unit is ₹ 5.
Answer:
Given,
Voltage (V) = 220 V
Power (P) = 1100 W
(a) Power (P) is given by the expression,
P = V × I
1100 = 220 × I
I = \(\frac{1100}{220}\)
= 5A
(b) Electrical energy (E)
\(\begin{aligned}
& =\frac{P(\text { in watt }) \times t(\text { in hour per day })}{1000} \times \text { No.of days } \\
& =\frac{1100 \mathrm{~W} \times(5 \mathrm{~h} / \text { day })}{1000} \times 6 \text { days }
\end{aligned}\)
= 33 units
(c) Total cost = Energy × Rate
= 33 units × \(\frac{\text { Rs. } 5}{\text { unit }}\) = Rs. 165
Question 33.
For the current-carrying solenoid as shown, draw magnetic field lines and give a reason to explain that out of the three points A, B and C, at which point the field strength is maximum and at which point is it minimum?
Answer:
(i) The field strength will be maximum at point A as A is inside the solenoid where the field lines have the highest density.
(ii) The field strength will be minimum at point B as field lines have the least density.
Section – D (15 marks)
(Q.no. 34 to 36 are long answer questions.)
Question 34.
(a) Draw the structure of the following components.
(i) Butanoic acid
(ii) Chloropentane
Answer:
(i) The structure of butanoic acid is:
(ii) The structure of chloropentane is:
(b) How are structure (i) and structure (ii) given below related to one another? Give a reason to justify your answer.
Draw one more possible structure for the above case.
Answer:
Structures (i) and (ii) are structural isomers of each other as they have different structures but same molecular formula (C6H14).
Another structural isomer is n-Hexane.
(c) Differentiate between saturated and unsaturated compounds on the basis of their general formula.
Answer:
Differences between saturated and unsaturated compounds are:
Saturated compounds | Unsaturated compounds |
They have single bonds between carbon atoms. | They have at least one double or triple bond between carbon atoms. |
Their general formula is CnH2n+2. | Alkenes (which have double bond) have general formula as CnH2n. Alkynes (which have triple bond) have general formula as CnH2n-2. |
OR
(a) What happens when a small piece of sodium is dropped on ethanol? Write the equation for this reaction.
(b) Why glacial acetic acid is called so?
(c) What happens when ethanol is heated at 443 K in the presence of conc. H2SO4? Write the role of conc. H2SO4 in this case.
(d) Write an equation showing saponification.
Answer:
(a) Ethanol reacts with sodium to produce hydrogen gas and sodium ethoxide.
2CH3CH2OH (Ethanol) + 2Na (Sodium) → 2CH3CH2O–Na+ (Sodium ethoxide) + H2 (Hydrogen gas)
(b) The freezing point of pure ethanoic acid is 290 K and hence, it freezes during winter in cold climates. That is why it is called glacial acetic acid.
(c) When ethanol is heated with concentrated sulphuric acid at 443 K, it loses one water molecule and forms ethene.
Role of H2SO4: It acts as a dehydrating agent and removes water molecules from ethanol.
(d) Equation for saponification reaction: Heat
Question 35.
(a) “Use of a condom is beneficial for both the sexes involved in a sexual act.” Justify this statement by giving two reasons.
(b) How does oral contraceptives help in avoiding pregnancies?
(c) What is sex selective abortion? How does it affect a healthy society? (State any one consequence)
Answer:
(a) Two reasons:
(i) Avoids unwanted/undesirable pregnancies / STDs.
(ii) Use of condoms prevents the transmission of infections from one person to another.
(b) Oral contraceptives change the hormonal balance of the body so that the eggs are not released.
(c) Sex-selective abortion is a procedure that is done for female foetuses/female foeticide. It adversely affects the male-female sex ratio.
OR
(a) Draw the diagram of the female reproductive system and match and mark the part(s):
(i) Where block is created surgically to prevent fertilisation.
(ii) Where is CuT inserted?
(iii) Inside which condom can be placed.
Answer:
Correct diagram with correct labelling, correctly matched with the following parts:
(i) Fallopian Tube/oviduct
(ii) Uterus
(iii) Vagina
(b) Why do more and more people prefer to use condoms? What is the principle behind the use of condoms?
Answer:
People prefer the use of condoms as it prevents STDs/gives privacy to the user. Condoms help create a mechanical barrier preventing the meeting of sperm and ovum.
Question 36.
(a) A lens produces a magnification of -0.5. Is this a converging or diverging lens? If the focal length of the lens is 6 cm; draw a ray diagram showing the image formation in this case.
Answer:
The image will be real and inverted since the magnification has negative value. The lens that can produce a real and inverted image is a converging/ convex lens.
In the figure OF1 = OF2 = 6 cm.
(Marks will be deducted if arrows are not shown)
(b) A girl was playing with a thin beam of light from a laser torch by directing it from different directions on a convex lens held vertically. She was surprised to see that in a particular direction, the beam of light continued to move along the same direction after passing through the lens. State the reason for her observation. Draw a ray diagram to support your answer.
Answer:
The girl must have directed the ray of light along the direction of the optical centre of the lens because the ray of light passes straight through the optical centre of the lens.
Section – E (12 Marks)
(Q.no. 37 to 39 are case-based/data-based questions with 2 to 3 short sub-parts.)
(Internal choice is provided in one of these sub-parts.)
Question 37.
Two students decided to investigate the effect of water and air on iron object under identical experimental conditions. They measured the mass of each object before placing it partially immersed in 10 mL of water. After a few days, the objects were removed, dried and their masses were measured. The table shows their results.
Student | Object | Mass of object before rusting in g |
Mass of the coated object in g |
A | Nail | 3.0 | 3.15 |
B | Thin plate | 6.0 | 6.33 |
(a) What might be the reason for the varied observations of the two students?
(b) In another set up the students coated iron nails with zinc metal and noted that iron nails coated with zinc prevent rusting. They also observed that zinc initially acts as a physical barrier, but an extra advantage of using zinc is that it continues to prevent rusting even if the layer of zinc is damaged. Name this process of rust prevention and give any two other methods to prevent rusting.
Answer:
(a) Rusting occurs in both A and B so there is an increase in mass.
As the surface area of B is more, the extent of rusting is more.
(b) Galvanisation
Oiling/greasing/painting/alloying/chromium plating or any other. (any two 1/2 mark each)
OR
(b) In which of the following applications of iron, rusting will occur most? Support your answer with a valid reason.
Answer:
Iron hinges on a gate.
Tron is in contact with atmospheric oxygen and moisture/water vapour.
Question 39.
A plant with red flower (Rw) is cross bred with a plant with white flower (ww). There are two variations of the gene controlling the colour of the flower. The gene for red flower (R) is dominant over that for white flower (w).
The Punnett square shows the result of the cross.
w | w | |
R | Rw | Rw |
w | ww | ww |
(a) What percentage of the plants is likely to produce white flowers?
(b) A red flower plant (RR) was crossed with a white flower plant (ww). What will be the colour of the flower of the next generation of plants?
(c) What would have caused the variation in the gene for flower colour?
Answer:
(a) In a cross between a plant with a red flower (Rw) and a plant with a white flower (ww), 50% of plants is likely to produce red flower and 50% white flowers.
(b) All flowers in the next generation would be red as R is the dominant trait. The flowers will inherit Rw set of genes.
(c) Mutation caused variation in the gene for flower colour. A mutation is a change in the DNA sequence of an organism. It can result from errors in DNA replication during cell division, exposure to mutagens or a viral infection.
OR
(c) What is the name given to the above cross? Define it.
Answer:
A cross between two plants, which differ in only one pair of contrasting characters, is called monohybrid cross. In this cross, F2 phenotypic ratio is 3:1 and genotypic ratio is 1:2:1.
Question 39.
Electrical resistivity is the electrical resistance of a specific specimen of the material of unit length and unit cross-sectional area. The electrical resistivity shows the current opposing property of a conductor. The table shows four different materials and their resistivity.
Material | Resistivity |
Material 1 | 1.62 × 10-8 |
Material 2 | 100 × 10-6 |
Material 3 | 6.84 × 10-8 |
Material 4 | 44 × 10-6 |
(a) Name the material, which is the best conductor of electricity?
(b) What is the SI unit of resistivity?
(c) Why is nichrome wire used in many electrical heating devices? Give two reasons.
Answer:
(a) Material 1 is the best conductor of electricity. Good conductors have high conductivity and low resistivity.
(b) The SI unit of resistivity is ohm-meter (Ω m).
(c) Nichrome wire is generally used as a heating element in heating appliances as:
(i) It offers a very large resistance. So a large amount of electric energy is converted into a large amount of heat energy.
(ii) It has a high melting point such that it can be heated till red hot without melting.
OR
(c) Name the element, which can be used for electrical transmission lines. Give reason.
Answer:
Copper, because it is economical, less oxidative than other metals and has low resistivity.