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Board exam practice paper
CBSE · Class 10 · Science (086)

Science: Board Exam Practice Paper

Time allowed: 3 hours · Maximum marks: 80 · AW-10S-BP-70086

Name: Date: Score: ____ / 80
  1. This paper has 39 questions in three sections: Section A is Biology, Section B is Chemistry and Section C is Physics.
  2. All questions are compulsory. Some questions have an internal choice (marked OR): answer only one of them.
  3. Each section has multiple-choice and assertion–reason questions of 1 mark, short answers of 2 and 3 marks, a case-based question of 4 marks (sub-parts of 1, 1 and 2 marks) and a long answer of 5 marks.
  4. Write each answer to fit its marks: about 30 to 50 words for 2 marks, 50 to 80 words for 3 marks and 80 to 120 words for 5 marks.
  5. Draw neat, labelled diagrams wherever asked.
Section A: Biology (30 marks)
1.
[1]A student counts 12 pulse beats in 10 seconds. The heart rate is:
  1. 82 beats per minute
  2. 72 beats per minute
  3. 12 beats per minute
  4. 120 beats per minute
2.
[1]Which of these has the job to carry water and minerals from the roots to the leaves?
  1. The anal sphincter
  2. Bile
  3. The xylem
  4. Haemoglobin
3.
[1]A nerve impulse travels 1.2 m along a neuron at 25 m/s. The time taken is:
  1. 30 ms
  2. 480 ms
  3. 48 ms
  4. 4.8 ms
4.
[1]In the human body, which of these carries the egg from the ovary; fertilisation takes place here?
  1. The vagina
  2. The ovaries
  3. The oviduct (fallopian tube)
  4. The scrotum
5.
[1]Potato usually reproduces asexually by:
  1. binary fission
  2. fragmentation
  3. vegetative propagation
  4. spore formation
6.
[1]A pure-breeding plant with axial flowers is crossed with a pure-breeding plant with terminal flowers, and the F1 plants are self-pollinated. Out of 232 F2 plants, about how many have terminal flowers?
  1. 116
  2. 232
  3. 174
  4. 58
7.
[1]The flow of energy in an ecosystem is:
  1. circular
  2. in one direction only (unidirectional)
  3. random
  4. in both directions
8.
[1]Assertion (A): If the kidneys filter 170 litres of fluid in a day and 2 litres leave as urine, about 98.82% of the filtrate is reabsorbed.
Reason (R): Most of the filtrate, including water, glucose and salts, is reabsorbed in the kidney tubules.
  1. Both A and R are true, and R is the correct explanation of A.
  2. Both A and R are true, but R is not the correct explanation of A.
  3. A is true, but R is false.
  4. A is false, but R is true.
9.
[1]Assertion (A): In the food chain grass → deer → lion, if the producers hold 10,000 J, the lion gets about 100 J.
Reason (R): Decomposers break down the dead remains of plants and animals.
  1. Both A and R are true, and R is the correct explanation of A.
  2. Both A and R are true, but R is not the correct explanation of A.
  3. A is true, but R is false.
  4. A is false, but R is true.
10.
[2]A strip of black paper is fixed across a leaf of a destarched hibiscus plant, which is then kept in sunlight for 5 hours. The leaf is tested with iodine. (a) What will the iodine test show? (b) What does this show about photosynthesis?
11.
[2]Distinguish between abscisic acid and auxin on the basis of (i) the effect on growth and (ii) an effect that can be seen.
OR
[2]Distinguish between transpiration and translocation on the basis of (i) what moves and (ii) where it happens.
12.
[2]Distinguish between regeneration and fragmentation on the basis of (i) the cells involved and (ii) an example.
13.
[3]A red blood cell travels from the left atrium to the right atrium by the shortest route. (a) Name, in order, the chambers of the heart, blood vessels and organs it passes through. (b) Which of the chambers and vessels on this route (including where it starts and ends) carry oxygenated blood, and which carry deoxygenated blood? (c) Why is it useful that the right and left sides of the heart are kept separate?
14.
[3]In the food chain plants → caterpillar → lizard → snake → hawk: The producers (the plants) hold 1,000 kJ of energy. (a) Using the 10 per cent law, find the energy available to each consumer in the chain. (b) What percentage of the energy held by the plants reaches the hawk? (c) Why is the flow of energy in a food chain said to be unidirectional?
OR
[3]Answer these questions about the ozone layer. (a) Name one harmful effect on human beings of more ultraviolet radiation reaching the Earth. (b) When did the amount of ozone in the atmosphere begin to drop sharply? (c) What step did countries take in 1987 to protect the ozone layer?
15.
A pea-plant experiment
For a school project, Rahul grows two pure-breeding lines of pea plants: plants with round seeds and plants with wrinkled seeds. Rahul dusts pollen from the plants with round seeds onto the stigmas of the plants with wrinkled seeds and raises 43 F1 plants from the seeds. The F1 plants are left to self-pollinate, and Rahul raises 532 F2 offspring from them. In pea plants, R = round, r = wrinkled.
(i)
[1]What are the genotype and the phenotype of the F1 plants?
(ii)
[1]About how many of the 532 F2 offspring are expected to be wrinkled?
(iii)
[2]Give the genotypes of the F2 offspring with their ratio, and the expected number of each.
OR
[2]How many of the round F2 offspring are expected to be pure-breeding (RR)? Why can Rahul not pick them out just by looking at them?
16.
[5](a) Name the method of asexual reproduction in each of these organisms and describe how it takes place: (i) Spirogyra, (ii) yeast, (iii) Leishmania. (b) Why do the offspring of asexual reproduction look almost exactly like the parent, and why is a little variation still seen?
OR
[5]The body cells of a frog have 26 chromosomes. (a) How many chromosomes are there in (i) each of its gametes (a sperm and an egg) and (ii) the zygote formed at fertilisation? (b) Gametes are made by a special division that halves the chromosome number. If they were made by ordinary division instead, how many chromosomes would a body cell have after 4 generations? (c) Why is the copying of DNA essential in reproduction, and why are the copies not always exactly alike? (d) Which kind of reproduction, sexual or asexual, produces more variation, and why?
Section B: Chemistry (25 marks)
17.
[1]The reaction Zn + H2SO4 → ZnSO4 + H2 is an example of:
  1. a combination reaction
  2. a double displacement reaction
  3. a displacement reaction
  4. a decomposition reaction
18.
[1]Solutions of barium chloride (BaCl2) and dilute sulphuric acid (H2SO4) are mixed. The precipitate formed is:
  1. H2SO4
  2. NaCl
  3. BaCl2
  4. BaSO4
19.
[1]What colour is red litmus in sodium hydroxide solution?
  1. pink
  2. green
  3. red
  4. blue
20.
[1]Solutions P, Q, R and S have pH values of 1, 2, 10, 12 respectively. Which is the most acidic?
  1. S
  2. Q
  3. P
  4. R
21.
[1]The oxide Fe2O3 is:
  1. basic
  2. amphoteric
  3. neutral
  4. acidic
22.
[1]Which of these will decolourise bromine water?
  1. C2H4
  2. C2H5COOH
  3. C3H7OH
  4. C4H9Cl
23.
[1]Soaps do not work well in hard water because they:
  1. become acidic
  2. form an insoluble scum with calcium and magnesium ions
  3. dissolve too quickly
  4. evaporate
24.
[1]Assertion (A): A solution with a pH of 10 is basic.
Reason (R): A pH below 7 means a solution is acidic, and a pH above 7 means it is basic.
  1. Both A and R are true, and R is the correct explanation of A.
  2. Both A and R are true, but R is not the correct explanation of A.
  3. A is true, but R is false.
  4. A is false, but R is true.
25.
[2]Rohan notices a reddish-brown, flaky coating on the chain of a bicycle at home. (a) Name this process and the substance formed, and state the two conditions needed for it. (b) Suggest a way to prevent it for the chain of a bicycle, and explain how the method works.
26.
[3]Dev adds dilute nitric acid to magnesium carbonate powder in a test tube and passes the gas given off through lime water. (a) Write the balanced chemical equation for the reaction in the test tube and name the salt formed. (b) Name the gas, state what happens to the lime water, and write the equation for this change. (c) Write a general word equation for the reaction of an acid with a metal carbonate or hydrogencarbonate.
OR
[3]Iron(III) chloride (FeCl3) is to be made by a neutralisation reaction. (a) Name the acid and the base it is formed from, and say whether each is strong or weak. (b) Write the balanced chemical equation for its formation. (c) Will a solution of iron(III) chloride in water have a pH less than 7, equal to 7 or more than 7? Give a reason.
27.
[3]A zinc strip is placed in copper sulphate solution (CuSO4) and left for some time. (a) Will a reaction take place? Give a reason. (b) Write the balanced chemical equation for the reaction. (c) Name a metal that could not displace copper from this solution, and give a reason.
28.
A burning feeling after dinner
After a heavy, spicy dinner at a wedding, Vikram complains of a burning feeling in the chest and pain in the stomach. The doctor explains that the stomach makes a dilute acid, with a pH of about 3, which helps to digest food, and that too much of it causes indigestion and pain. The doctor suggests a spoon of baking soda in water (NaHCO3), a mild base that is called an antacid.
(i)
[1]Name the acid made by the stomach.
(ii)
[1]Why is a mild base, and not a strong base such as sodium hydroxide, given as an antacid?
(iii)
[2]Write the balanced chemical equation for the reaction of the antacid with the stomach acid, and name this type of reaction.
OR
[2]Before the antacid, the stomach juice had a pH of about 3. Will the pH rise or fall after the antacid acts? Explain in terms of hydrogen ions.
29.
[5]Two hydrocarbons are P (C3H8) and Q (C3H6). (a) Which of them is saturated and which is unsaturated? Give a reason. (b) Q reacts with hydrogen in the presence of a nickel catalyst. Write the balanced equation and give one industrial use of this kind of reaction. (c) P reacts with chlorine in sunlight. Write the balanced equation for the first step and name the type of reaction. (d) Write the balanced equation for the complete combustion of P. (e) How could you tell P and Q apart using bromine water?
OR
[5]Butanoic acid (C3H7COOH) is warmed with ethanol (C2H5OH) and a few drops of concentrated sulphuric acid. (a) Write the balanced chemical equation and name the organic product. (b) What is the role of the concentrated sulphuric acid, and how could you tell that the product has formed? (c) The product is heated with sodium hydroxide solution. Write the balanced equation for this reaction. (d) Write the balanced equation for the reaction of butanoic acid with sodium hydrogencarbonate. (e) Name the gas given off in (d) and give a test for it.
Section C: Physics (25 marks)
30.
[1]The radius of curvature of a concave mirror is 12 cm. Its focal length is:
  1. −6 cm
  2. −12 cm
  3. −7 cm
  4. 6 cm
31.
[1]A charge of 225 C flows through a wire in 50 s. The current is:
  1. 11,250 A
  2. 5.5 A
  3. 4.5 A
  4. 0.22 A
32.
[1]Assertion (A): A current flowing towards the north in a magnetic field pointing east feels a force vertically downwards.
Reason (R): Magnetic field lines are closed curves.
  1. Both A and R are true, and R is the correct explanation of A.
  2. Both A and R are true, but R is not the correct explanation of A.
  3. A is true, but R is false.
  4. A is false, but R is true.
33.
[2]Meera passes white light through a glass prism and looks at the indigo and red parts of the spectrum on a screen. Which of the two is bent more by the prism? Give a reason.
34.
[2]Resistors of 19 Ω and 20 Ω are connected in series to a 78 V battery. Find the current in the circuit and the potential difference across the 19 Ω resistor.
OR
[2]A solenoid of 250 turns has ends L and M. Seen from end L, the current flows clockwise. (i) Which end behaves as a north pole? (ii) The current is now reversed. Does the north pole of a compass placed near end M point towards or away from end M?
35.
[3]Three resistors of 12 Ω, 16 Ω and 48 Ω are connected in parallel across a battery of 144 V. Find (i) the equivalent resistance, (ii) the current through each resistor, and (iii) the total current drawn from the supply.
36.
[3]A solenoid of 750 turns has ends A and B. When it is connected to a battery, the current, seen from end B, flows anticlockwise round the coil. (i) Which end of the solenoid behaves as a north pole? (ii) The north pole of a bar magnet is brought near end A. Is it attracted or repelled? (iii) Describe the magnetic field inside the solenoid, and give one way to make it stronger.
37.
[3]Three resistors of 18 Ω, 27 Ω and 54 Ω are connected in parallel across a DC supply of 216 V. Find (i) the equivalent resistance, (ii) the current through each resistor, and (iii) the total current drawn from the supply.
38.
Colours in the sky
During a weekend outing, Rohan watches the sun set from a beach. The sky overhead is blue, but the sun near the horizon looks reddish. On the way back, Rohan notices that the warning lamps at a road repair site are red. At home, Rohan passes a narrow beam of white light through a glass prism and sees a band of colours on a white wall.
(i)
[1]Of these colours, which is scattered the most by very fine particles in the air?
  1. yellow
  2. blue
  3. violet
  4. indigo
(ii)
[1]Why are signal and warning lights made red?
(iii)
[2]Why does the clear sky look blue from the ground? How would it look to an astronaut far above the atmosphere?
OR
[2]Why does the sun look reddish when it is near the horizon?
39.
[5]Light travels at 2.4 × 108 m/s in a gemstone (medium A) and at 1.5 × 108 m/s in a crystal (medium B). The speed of light in vacuum is 3 × 108 m/s. (a) Find the absolute refractive index of A and of B. (b) Find the refractive index of B with respect to A. (c) A ray of light passes obliquely from A into B. Does it bend towards or away from the normal? Give a reason. (d) A third medium C has a refractive index of 1.92 with respect to A. Find the speed of light in C. (Give answers to 2 decimal places where needed.)
OR
[5]A convex lens of focal length 20 cm is used to form a sharp, real image on a screen that is one-half the size of the object. (a) How far from the lens must the object be placed? (b) How far from the lens is the screen, and what is the distance between the object and the screen? (c) Find the power of the lens. (d) Describe the image if the object is then moved to a point between the lens and its principal focus.
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Marking scheme
CBSE · Class 10 · Science (086)

Marking scheme

Science: Board Exam Practice Paper · AW-10S-BP-70086 · For the parent or teacher: award the marks shown for each step, even when the final answer is wrong.

QAnswer and marks for each stepMarks
Section A: Biology (30 marks)
1(b) 72 beats per minute
12 × 60 ÷ 10
1
2(c) The xylem1
3(c) 48 ms
1.2 ÷ 25 s = 48 ms
1
4(c) The oviduct (fallopian tube)1
5(c) vegetative propagation1
6(d) 58
terminal : total = 1 : 4
1
7(b) in one direction only (unidirectional)
energy passing to the next level cannot come back
1
8(a) Both A and R are true, and R is the correct explanation of A.
A is true: (170 − 2) ÷ 170 × 100 = 98.82%. R is true and explains A.
1
9(b) Both A and R are true, but R is not the correct explanation of A.
A is true: 10,000 × (1/10)2 = 100 J. R is true but does not explain A.
1
10
  1. (a) The part that was covered does not turn blue-black; the uncovered part does. (1)
  2. (b) No starch is made where light cannot reach, so light is needed for photosynthesis. (1)
2
11
  1. (i) The effect on growth: abscisic acid — inhibits growth; auxin — promotes growth by making cells grow longer. (1)
  2. (ii) An effect that can be seen: abscisic acid — the wilting of leaves; auxin — a shoot bending towards light. (1)
2
11 OR
  1. (i) What moves: transpiration — water, lost as vapour from the leaves; translocation — food (the products of photosynthesis). (1)
  2. (ii) Where it happens: transpiration — mainly through the stomata of the leaves; translocation — through the phloem. (1)
2
12
  1. (i) The cells involved: regeneration — specialised cells divide and develop into all the different tissues; fragmentation — each piece of the simple body grows on. (1)
  2. (ii) An example: regeneration — Planaria; fragmentation — Spirogyra. (1)
2
13
  1. (a) The left atrium → the left ventricle → the aorta → the body organs → the vena cava → the right atrium. (1)
  2. (b) Oxygenated: the left atrium, the left ventricle, the aorta. Deoxygenated: the vena cava, the right atrium. (1)
  3. (c) It stops oxygenated and deoxygenated blood from mixing, so the body gets a highly efficient supply of oxygen; birds and mammals need this because they use a lot of energy to keep their body temperature constant. (1)
3
14
  1. (a) dividing by 10 at each step: caterpillar: 100 kJ; lizard: 10 kJ; snake: 1 kJ; hawk: 0.1 kJ. (1)
  2. (b) 0.01% (0.1 ÷ 1,000 × 100 = (1/10)4 × 100). (1)
  3. (c) Energy passes from the producers to the herbivores and on to the carnivores; energy that has passed to a higher level does not come back to the level below, and the energy captured by the producers does not return to the Sun. (1)
3
14 OR
  1. (a) It can cause skin cancer (it can also damage the eyes). (1)
  2. (b) In the 1980s. (1)
  3. (c) Under the United Nations Environment Programme (UNEP), they agreed to freeze CFC production at 1986 levels; making CFC-free refrigerators is now required throughout the world. (1)
3
15 (i)All are Rr and round.
  1. RR × rr: every F1 plant gets R from one parent and r from the other, and R is dominant — All are Rr and round. (1)
1
15 (ii)133
  1. Rr × Rr gives wrinkled offspring (rr) in 1 out of 4; 532 ÷ 4 — 133 (1)
1
15 (iii)RR : Rr : rr = 1 : 2 : 1; RR: 133, Rr: 266, rr: 133
  1. Each F1 plant makes R and r gametes; Punnett square Rr × Rr: RR, Rr, Rr, rr, so RR : Rr : rr = 1 : 2 : 1 (1)
  2. Out of 532: RR 133, Rr 266, rr 133 (1)
2
15 (iii) OR133 of the 399 round offspring; RR and Rr look the same because R is dominant.
  1. round offspring = 3/4 × 532 = 399, of which RR : Rr = 1 : 2, so 133 are RR (1)
  2. One copy of the dominant R is enough to give the round phenotype, so RR and Rr plants look alike (1)
2
16
  1. (i) Spirogyra: fragmentation — the mature filament breaks into small pieces, and each piece grows into a new filament. (1)
  2. (ii) Yeast: budding — a small outgrowth (bud) forms on the cell, grows and separates as a new cell. (1)
  3. (iii) Leishmania: binary fission — the cell divides into two in a definite plane, related to the whip-like structure at one end. (1)
  4. (b) They come from a single parent and receive copies of its DNA, so they are very similar to it. (1)
  5. DNA copying is not perfectly accurate, so small changes creep in and the offspring are not quite identical. (1)
5
16 OR
  1. (a)(i) 13 in each gamete (half of 26). (1)
  2. (a)(ii) 26 in the zygote (13 + 13). (1)
  3. (b) 416: the number would double in every generation, 26 × 24 = 416; halving in the gametes keeps it at 26 in every generation, so the DNA and body design stay stable. (1)
  4. (c) DNA carries the information for making the proteins that build the body design, so each new cell must get a copy. The copying reactions are not absolutely accurate, so small variations arise in the copies. (1)
  5. (d) Sexual reproduction combines the DNA of two parents, so it produces more variation in the offspring than asexual reproduction. (1)
5
Section B: Chemistry (25 marks)
17(c) a displacement reaction
a more reactive element replaces another from its compound
1
18(d) BaSO4
BaSO4 is insoluble in water
1
19(d) blue
sodium hydroxide solution is basic
1
20(c) P
the lowest pH is the most acidic (most H+ ions)
1
21(a) basic1
22(a) C2H4
unsaturated compounds (C=C or C≡C) add bromine
1
23(b) form an insoluble scum with calcium and magnesium ions1
24(a) Both A and R are true, and R is the correct explanation of A.
A is true: pH 10 is above 7, so the solution is basic. R is true and explains A.
1
25(a) Rusting (corrosion of iron); rust is hydrated iron(III) oxide. Both air (oxygen) and water (moisture) are needed. (b) Oiling or greasing it: the coating keeps air and moisture from reaching the iron.
  1. Rusting: hydrated iron(III) oxide; needs air and water (1)
  2. Oiling or greasing it — keeps out air and moisture (1)
2
26(a) MgCO3 + 2HNO3 → Mg(NO3)2 + H2O + CO2; the salt is magnesium nitrate. (b) Carbon dioxide; the lime water turns milky because insoluble calcium carbonate forms: Ca(OH)2 + CO2 → CaCO3 + H2O. (c) Metal carbonate (or hydrogencarbonate) + acid → salt + carbon dioxide + water.
  1. MgCO3 + 2HNO3 → Mg(NO3)2 + H2O + CO2 (magnesium nitrate) (1)
  2. Carbon dioxide turns lime water milky: Ca(OH)2 + CO2 → CaCO3 + H2O (1)
  3. Metal carbonate (or hydrogencarbonate) + acid → salt + carbon dioxide + water. (1)
3
26 OR(a) Hydrochloric acid (HCl, a strong acid) and iron(III) hydroxide (Fe(OH)3, a weak base). (b) Fe(OH)3 + 3HCl → FeCl3 + 3H2O. (c) pH less than 7, because a salt of a strong acid and a weak base is acidic.
  1. Parents: Hydrochloric acid (HCl, a strong acid) and iron(III) hydroxide (Fe(OH)3, a weak base) (1)
  2. Equation: Fe(OH)3 + 3HCl → FeCl3 + 3H2O (1)
  3. pH less than 7: a salt of a strong acid and a weak base is acidic (1)
3
27(a) Yes. Zinc is more reactive than copper (it is above copper in the reactivity series), so it displaces copper from its salt solution. (b) Zn + CuSO4 → ZnSO4 + Cu. (c) Mercury or gold (any metal below copper in the reactivity series): it is less reactive than copper.
  1. Yes — Zinc is more reactive than copper (it is above copper in the reactivity series), so it displaces copper from its salt solution (1)
  2. Zn + CuSO4 → ZnSO4 + Cu (1)
  3. Mercury or gold (any metal below copper in the reactivity series): it is less reactive than copper. (1)
3
28 (i)Hydrochloric acid (HCl)
  1. Hydrochloric acid (HCl) (the stomach produces dilute hydrochloric acid) (1)
1
28 (ii)A strong base is corrosive and would harm the lining of the mouth, food pipe and stomach; a mild base neutralises the extra acid safely.
  1. A strong base is corrosive and would harm the lining of the mouth, food pipe and stomach; a mild base neutralises the extra acid safely. (strong bases are corrosive) (1)
1
28 (iii)NaHCO3 + HCl → NaCl + H2O + CO2; neutralisation.
  1. Equation: NaHCO3 + HCl → NaCl + H2O + CO2 (1)
  2. Type: neutralisation (an acid reacts with a base to give a salt and water) (1)
2
28 (iii) ORIt rises (towards 7), because the antacid neutralises some of the acid, lowering the concentration of hydrogen ions.
  1. The pH rises towards 7 (1)
  2. The base neutralises part of the acid, so there are fewer hydrogen ions; fewer hydrogen ions means a higher pH (1)
2
29(a) P (propane) is saturated: it has only single bonds between carbon atoms. Q (propene) is unsaturated: it has a double bond. (b) C3H6 + H2 → C3H8; an addition (hydrogenation) reaction, used to turn vegetable oils into solid fats such as vanaspati. (c) C3H8 + Cl2 → C3H7Cl + HCl; a substitution reaction (one hydrogen atom is replaced by chlorine). (d) C3H8 + 5O2 → 3CO2 + 4H2O. (e) Q decolourises the orange-brown bromine water (it adds bromine across its double bond); P does not.
  1. P saturated (single bonds), Q unsaturated (double bond) (1)
  2. C3H6 + H2 → C3H8 — hydrogenation of vegetable oils (1)
  3. C3H8 + Cl2 → C3H7Cl + HCl — substitution (1)
  4. C3H8 + 5O2 → 3CO2 + 4H2O (1)
  5. Q decolourises the orange-brown bromine water (it adds bromine across its double bond); P does not. (1)
5
29 OR(a) C3H7COOH + C2H5OH → C3H7COOC2H5 + H2O; ethyl butanoate, an ester. (b) It acts as a catalyst (and removes the water formed); the ester has a sweet, fruity smell. (c) C3H7COOC2H5 + NaOH → C3H7COONa + C2H5OH; sodium butanoate and ethanol are formed. (d) C3H7COOH + NaHCO3 → C3H7COONa + H2O + CO2. (e) Carbon dioxide; it turns lime water milky.
  1. C3H7COOH + C2H5OH → C3H7COOC2H5 + H2O (ethyl butanoate) (1)
  2. Catalyst; sweet fruity smell of the ester (1)
  3. C3H7COOC2H5 + NaOH → C3H7COONa + C2H5OH (sodium butanoate + ethanol) (1)
  4. C3H7COOH + NaHCO3 → C3H7COONa + H2O + CO2 (1)
  5. Carbon dioxide; it turns lime water milky. (1)
5
Section C: Physics (25 marks)
30(a) −6 cm
f = R/2, negative for a concave mirror
1
31(c) 4.5 A
I = Q ÷ t = 225 ÷ 50
1
32(b) Both A and R are true, but R is not the correct explanation of A.
A is true: the force is vertically downwards. R is true but does not explain A.
1
33Indigo is bent more than red: different colours travel at different speeds in glass, and indigo light (shorter wavelength) is slowed and bent more
  1. Indigo is bent more, red less (in the spectrum indigo lies nearer the violet end) (1)
  2. The refractive index of glass is different for each colour; it is larger for indigo, so indigo bends more (1)
2
342 A; 38 V
  1. In series R = 19 + 20 = 39 Ω, so I = V/R = 78 ÷ 39 = 2 A (1)
  2. The same current flows through each resistor: V = IR = 2 × 19 = 38 V (1)
2
34 OR(i) End M; (ii) Towards end M, which is now a south pole
  1. The end where the current is seen to flow anticlockwise is the north pole: end M (1)
  2. Reversing the current swaps the poles, so end M becomes a south pole and the compass's north pole points towards it (1)
2
35(i) 6 Ω; (ii) 12 A, 9 A and 3 A; (iii) 24 A
  1. 1/R = 1/12 + 1/16 + 1/48 = 1/6, so R = 6 Ω (1)
  2. Each resistor has the full 144 V across it: I = V/R gives 144 ÷ 12 = 12 A, 144 ÷ 16 = 9 A, 144 ÷ 48 = 3 A (1)
  3. Total I = 12 + 9 + 3 = 24 A (= 144 ÷ 6) (1)
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36(i) End B; (ii) Attracted, because end A is a south pole; (iii) Inside, the field lines are parallel straight lines, so the field is uniform; it can be made stronger by increasing the current (or the number of turns, or by putting a soft iron core inside)
  1. The end at which the current is seen to flow anticlockwise is the north pole, so end B is north and end A is south (1)
  2. End A is a south pole; unlike poles attract, so the magnet is attracted (1)
  3. Inside, the field lines are parallel straight lines, so the field is uniform; it can be made stronger by increasing the current (or the number of turns, or by putting a soft iron core inside) (1)
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37(i) 9 Ω; (ii) 12 A, 8 A and 4 A; (iii) 24 A
  1. 1/R = 1/18 + 1/27 + 1/54 = 1/9, so R = 9 Ω (1)
  2. Each resistor has the full 216 V across it: I = V/R gives 216 ÷ 18 = 12 A, 216 ÷ 27 = 8 A, 216 ÷ 54 = 4 A (1)
  3. Total I = 12 + 8 + 4 = 24 A (= 216 ÷ 9) (1)
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38 (i)(c) violet
  1. the shorter the wavelength, the more the scattering — violet (1)
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38 (ii)
  1. Red light has the longest wavelength, so it is scattered the least by fog, smoke and dust and can be seen from far away (1)
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38 (iii)The fine particles of air scatter blue light (shorter wavelength) much more than red, and this scattered blue light reaches our eyes; above the atmosphere there is no scattering, so the sky looks dark
  1. Particles of air smaller than the wavelength of light scatter blue light much more than red (1)
  2. Above the atmosphere there is nothing to scatter light, so the sky looks dark (1)
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38 (iii) ORNear the horizon, sunlight passes through a much thicker layer of air; most of the blue light of shorter wavelength is scattered away, so the light that reaches us is mostly red, of longer wavelength
  1. Near the horizon, sunlight travels a long path through the air (1)
  2. shorter wavelengths (blue) are scattered away; the longer red wavelength reaches the eye (1)
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39(a) n_A = 1.25, n_B = 2; (b) n_BA = 1.6; (c) towards the normal, because light travels slower in B (B is optically denser); (d) 1.25 × 108 m/s
  1. n_A = c/v_A = 3 ÷ 2.4 = 1.25 (1)
  2. n_B = c/v_B = 3 ÷ 1.5 = 2 (1)
  3. n_BA = v_A/v_B = 2.4 ÷ 1.5 = 1.6 (1)
  4. v_B < v_A, so B is optically denser and the ray bends towards the normal (1)
  5. n_CA = v_A/v_C, so v_C = 2.4 ÷ 1.92 = 1.25 × 108 m/s (1)
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39 OR(a) 60 cm from the lens (u = −60 cm); (b) 30 cm; the object and screen are 90 cm apart; (c) +5 D; (d) virtual, erect and magnified, on the same side of the lens as the object (it cannot be taken on a screen)
  1. A real image is inverted, so m = v/u = −1/2, giving v = −u/2 (1)
  2. 1/v − 1/u = 1/f gives u = −60 cm, so the object is 60 cm from the lens (1)
  3. v = 30 cm; distance between object and screen = 30 + 60 = 90 cm (1)
  4. P = 100 ÷ 20 = +5 D (1)
  5. Between F and the lens the image is virtual, erect and magnified, on the same side as the object (1)
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