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SOF NSO study materials
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SOF NSO practice questions

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Question 1Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

Which property explains why metals such as copper and aluminium are used to make electrical transmission wires?

  1. They conduct electricity and are ductile enough to be drawn into wires Correct answer.
  2. They have high melting points and are sonorous
  3. They are good reducing agents that displace hydrogen from acids
  4. They are malleable and can be hammered into thin sheets

Explanation

Metals have delocalised electrons that carry current, so they conduct electricity well, and their ductility lets them be drawn into long wires without breaking. Malleability, sonority and reducing behaviour are genuine metal properties but do not explain the choice for transmission wires.

Question 2Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

When a piece of sodium is dropped into water, it floats and moves rapidly on the surface. Which set of observations best describes the reaction?

  1. It sinks and releases a gas slowly with a blue flame
  2. It dissolves quietly without any gas being produced
  3. It floats, melts into a silvery ball, releases hydrogen and may catch fire Correct answer.
  4. It reacts only after heating and forms a white precipitate

Explanation

Sodium is less dense than water and its reaction is strongly exothermic, so the metal melts into a shiny ball that darts about while hydrogen gas is released, often igniting. The reaction is fast and does not need heating.

Question 3Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

A covalent compound of carbon and hydrogen burns in oxygen to give carbon dioxide and water only. Which class does this compound belong to?

  1. A ketone such as propanone
  2. An alcohol such as ethanol
  3. A hydrocarbon such as methane Correct answer.
  4. A carboxylic acid such as ethanoic acid

Explanation

A compound made only of carbon and hydrogen is a hydrocarbon, and complete combustion of any hydrocarbon gives carbon dioxide and water. Ethanol and carboxylic acids contain oxygen, so their combustion products alone would not prove the composition.

Question 4Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

In a flowering plant, which structure develops into the fruit after fertilisation?

  1. The ovary Correct answer.
  2. The stigma
  3. The anther
  4. The style

Explanation

After fertilisation the ovules become seeds and the ovary wall thickens to form the fruit. The style, stigma and anther are parts of the flower that wither or are shed rather than becoming the fruit.

Question 5Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

A resistor of 6 ohm is connected across a 12 V battery. What current flows through it?

  1. 0.5 A
  2. 6 A
  3. 2 A Correct answer.
  4. 72 A

Explanation

Ohm's law states that current equals potential difference divided by resistance, so 12 V divided by 6 ohm gives 2 A. Multiplying the two values instead of dividing gives the wrong result.

Question 6Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

Which rule correctly gives the direction of the magnetic field around a straight current-carrying conductor?

  1. The field forms concentric circles around the wire, given by the right-hand thumb rule Correct answer.
  2. The field points radially outward from the wire like spokes
  3. The field lines run parallel to the wire along the current direction
  4. The field exists only at the two ends of the wire

Explanation

A straight conductor produces a magnetic field in the form of concentric circles in a plane perpendicular to the wire, and the right-hand thumb rule gives the sense of these circles. The field is not parallel to the wire, radial, or confined to the ends.

Question 7Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

Which part of the human brain mainly maintains posture and balance during walking?

  1. Hypothalamus
  2. Cerebrum
  3. Cerebellum Correct answer.
  4. Medulla oblongata

Explanation

The cerebellum coordinates voluntary movements and controls balance and posture. The cerebrum handles thinking and memory, the medulla controls involuntary actions such as breathing, and the hypothalamus regulates body temperature and hunger.

Question 8Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

Which of these substances is a non-metal that conducts electricity at room temperature?

  1. Sodium
  2. Iodine
  3. Sulphur
  4. Graphite Correct answer.

Explanation

Graphite is an allotrope of carbon in which each carbon atom bonds to three others, leaving one delocalised electron per atom to carry current. Sulphur and iodine are non-metals that do not conduct, and sodium is a metal.

Question 9Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

Ethanoic acid is added to sodium carbonate in a test tube. Which observation confirms that a carboxylic acid is present?

  1. A sweet smell is produced immediately
  2. The mixture turns blue litmus paper red only after heating
  3. A white precipitate settles at the bottom
  4. Effervescence of a gas that turns lime water milky Correct answer.

Explanation

Carboxylic acids react with carbonates to release carbon dioxide, which turns lime water milky. The brisk effervescence is the characteristic test, whereas a precipitate or a smell is not a reliable indicator.

Question 10Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

A metal M displaces zinc from zinc sulphate solution but does not displace copper from copper sulphate solution. Where is M most likely placed in the reactivity series?

  1. Below copper
  2. Between zinc and copper Correct answer.
  3. Exactly at the position of copper
  4. Above zinc

Explanation

A metal can displace another only if it is more reactive, so M is above zinc but below copper in the series. Being above zinc would let it displace copper as well, and being below copper would prevent both displacements.

Question 11Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

In the electrolysis of acidified water using platinum electrodes, what is observed at the cathode and at the anode?

  1. Hydrogen at the cathode, oxygen at the anode, in a 2:1 volume ratio Correct answer.
  2. Hydrogen at both electrodes
  3. Oxygen at both electrodes
  4. Oxygen at the cathode, hydrogen at the anode, in a 1:2 volume ratio

Explanation

At the cathode, hydrogen ions gain electrons to form hydrogen gas, while at the anode water is oxidised to oxygen. Because water contains two hydrogen atoms for each oxygen atom, the volume of hydrogen collected is twice that of oxygen.

Question 12Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

Carbon shows the property of catenation strongly, which allows it to form a vast number of compounds. What does catenation mean?

  1. The ability of an element to bond with itself forming chains Correct answer.
  2. The ability to exist in two crystalline forms
  3. The ability to displace hydrogen from acids
  4. The ability of an atom to gain electrons in a reaction

Explanation

Catenation is self-linking: carbon atoms bond to one another to form straight chains, branched chains and rings. This, combined with tetravalency, explains the huge number of carbon compounds.

Question 13Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

Ethanol is warmed with excess alkaline potassium permanganate until the colour of the solution disappears. What is the main organic product?

  1. Ethanoic acid Correct answer.
  2. Methane
  3. Ethyl ethanoate
  4. Ethene

Explanation

Alkaline potassium permanganate is an oxidising agent that converts the alcohol ethanol first to ethanal and then to ethanoic acid, decolourising the solution. Ethene would require dehydration with concentrated sulphuric acid, and the ester needs an acid catalyst.

Question 14Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

Which statement correctly compares the number of chromosomes in a human body cell and a human gamete?

  1. The body cell has 23 and the gamete has 46
  2. Both have 46 chromosomes
  3. The body cell has 46 and the gamete has 23 Correct answer.
  4. The body cell has 46 and the gamete has 46 pairs

Explanation

Human body cells are diploid with 46 chromosomes, arranged as 23 pairs. Gametes are formed by meiosis and are haploid, carrying 23 chromosomes so that fusion restores the diploid number.

Question 15Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

In a cross between two heterozygous tall pea plants (Tt), what fraction of the offspring is expected to show the recessive short phenotype?

  1. 3/4
  2. 1/4 Correct answer.
  3. 1/2
  4. 0

Explanation

A Tt x Tt cross gives genotypes TT, Tt, Tt and tt in equal proportions, so only one of four offspring is tt and shows the recessive trait. Three of four carry at least one dominant T and are tall.

Question 16Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

Two resistors of 4 ohm and 6 ohm are joined in parallel across a 12 V supply. What is the total current drawn from the supply?

  1. 10 A
  2. 5 A Correct answer.
  3. 2 A
  4. 1.2 A

Explanation

In parallel, each resistor receives the full 12 V, so the currents are 12/4 = 3 A and 12/6 = 2 A, giving a total of 5 A. The equivalent resistance is 2.4 ohm, and 12 V divided by 2.4 ohm also gives 5 A.

Question 17Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

An electric iron marked 220 V, 1100 W is used on a 220 V supply. What is its resistance?

  1. 242000 ohm
  2. 0.2 ohm
  3. 5 ohm
  4. 44 ohm Correct answer.

Explanation

Power equals voltage squared divided by resistance, so resistance equals 220 squared divided by 1100, which is 48400/1100 = 44 ohm. The current is 5 A, and 220 V divided by 5 A confirms 44 ohm.

Question 18Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

Why is the magnetic field inside a long current-carrying solenoid uniform and strong?

  1. Because the field of each turn adds up along the axis inside the coil Correct answer.
  2. Because the current becomes zero inside the coil
  3. Because the solenoid cancels the field of the Earth
  4. Because the wire is insulated

Explanation

Inside a solenoid the circular fields of many turns point in the same direction along the axis, so they reinforce one another to give a strong, uniform field. Insulation only prevents short-circuiting between turns and does not create the field.

Question 19Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

A current-carrying conductor is placed in a magnetic field at right angles to the field. Which change would reverse the direction of the force on it?

  1. Making the conductor thicker
  2. Reversing the direction of the current only Correct answer.
  3. Placing the conductor parallel to the field
  4. Increasing the current in the conductor

Explanation

The force direction is given by Fleming's left-hand rule and depends on the directions of the current and the field. Reversing the current reverses the force, whereas increasing current or thickness changes only its magnitude.

Question 20Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

Which sequence correctly describes the path of a nerve impulse in a reflex action?

  1. Receptor, motor neuron, spinal cord, sensory neuron, effector
  2. Spinal cord, receptor, sensory neuron, effector, motor neuron
  3. Effector, motor neuron, spinal cord, sensory neuron, receptor
  4. Receptor, sensory neuron, spinal cord, motor neuron, effector Correct answer.

Explanation

A reflex arc begins at the receptor, travels along the sensory neuron to the spinal cord, crosses a synapse to the motor neuron and ends at the effector muscle or gland. This short route allows a quick response without waiting for the brain.

Question 21Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

Which statement correctly describes the role of abscisic acid in a plant under water stress?

  1. It induces ripening of fruits
  2. It promotes cell elongation in the stem
  3. It stimulates root initiation from cuttings
  4. It causes stomatal closure and slows growth Correct answer.

Explanation

Abscisic acid is a stress hormone that closes stomata to reduce water loss and inhibits growth when conditions are unfavourable. Cell elongation is promoted by auxins, ripening by ethylene and root initiation by auxins.

Question 22Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

A metal carbonate decomposes on heating to give a metal oxide and carbon dioxide. Which pair of carbonates both decompose in this way on strong heating?

  1. Potassium carbonate and magnesium carbonate
  2. Sodium carbonate and potassium carbonate
  3. Calcium carbonate and magnesium carbonate Correct answer.
  4. Sodium carbonate and calcium carbonate

Explanation

Carbonates of fairly reactive metals such as calcium and magnesium decompose on heating into the oxide and carbon dioxide. Sodium and potassium carbonates are stable to heat and do not decompose in the same way.

Question 23Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

An organic compound X of molecular formula C2H4O2 gives brisk effervescence with sodium hydrogen carbonate and forms a sweet-smelling compound with ethanol in the presence of a little concentrated sulphuric acid. What is X?

  1. Ethanol
  2. Ethanoic acid Correct answer.
  3. Ethyl ethanoate
  4. Ethanal

Explanation

Effervescence with sodium hydrogen carbonate identifies a carboxylic acid, and C2H4O2 fits ethanoic acid. Its reaction with ethanol under acid catalysis gives the ester ethyl ethanoate, which accounts for the sweet smell.

Question 24Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

A pea plant heterozygous for a dominant trait is crossed with a plant showing the recessive trait, and half the offspring show the recessive phenotype. Which conclusion follows?

  1. The recessive phenotype appears only when the dominant allele is absent Correct answer.
  2. The dominant parent must be homozygous
  3. The recessive parent must be heterozygous
  4. The trait is not controlled by alleles

Explanation

A recessive phenotype is expressed only when both alleles are recessive, so it appears in the offspring only when no dominant allele is inherited. A test cross of a heterozygote with a recessive homozygote gives a 1:1 ratio, matching the observation.

Question 25Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

Two identical resistors are connected first in series and then in parallel across the same battery. How does the total power consumed compare in the two arrangements?

  1. The parallel arrangement consumes twice the power
  2. The parallel arrangement consumes four times the power Correct answer.
  3. The series arrangement consumes four times the power
  4. Both arrangements consume the same power

Explanation

Two equal resistors give a series resistance of 2R and a parallel resistance of R/2, a ratio of four. Since power equals voltage squared divided by resistance, the parallel arrangement consumes four times the power of the series one.

Question 26Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

Which property of metals is directly responsible for their use in making thin wires for electric circuits?

  1. Malleability
  2. Ductility Correct answer.
  3. Sonority
  4. Brittleness

Explanation

Ductility is the ability of a metal to be drawn into thin wires, which is exactly what is needed to make conducting wires. Malleability concerns beating into sheets, sonority concerns sound, and brittleness is a non-metal-like property of shattering.

Question 27Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

When sulphur dioxide is passed through moist blue litmus paper, the paper turns red. Which conclusion about sulphur dioxide is supported by this observation?

  1. It is an acidic oxide that dissolves in water to form an acid Correct answer.
  2. It is a neutral oxide with no effect on indicators
  3. It is a metal oxide that conducts electricity
  4. It is a basic oxide that neutralises acids

Explanation

Non-metal oxides such as sulphur dioxide dissolve in water to give acidic solutions, and acids turn blue litmus red. This is why the moist paper changes colour, showing the oxide is acidic in nature.

Question 28Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

Which allotrope of carbon is a good conductor of electricity because each carbon atom is bonded to only three others in layered sheets?

  1. Charcoal
  2. Graphite Correct answer.
  3. Diamond
  4. Fullerene

Explanation

In graphite each carbon atom forms three sigma bonds, leaving the fourth valence electron delocalised within the layers. These free electrons make graphite a conductor, while diamond's four bonds per atom leave no free electrons.

Question 29Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

Asexual reproduction in Hydra commonly takes place by which process?

  1. Binary fission
  2. Budding Correct answer.
  3. Fragmentation
  4. Spore formation

Explanation

Hydra reproduces asexually by budding, in which a small outgrowth forms on the body and develops into a new individual before detaching. Binary fission is typical of Amoeba, fragmentation of Spirogyra, and spore formation of Rhizopus.

Question 30Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

In a domestic electric circuit, which wire is connected to the earth and provides a low-resistance path for leakage current?

  1. The live wire
  2. The neutral wire
  3. The fuse wire
  4. The earth wire Correct answer.

Explanation

The earth wire is connected to a metal plate buried in the ground and provides a safe path for current if the metal casing of an appliance becomes live. This prevents a severe shock to the user.

Question 31Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

Which part of the human eye controls the amount of light entering it by changing the size of the pupil?

  1. Iris Correct answer.
  2. Optic nerve
  3. Retina
  4. Cornea

Explanation

The iris is the muscular coloured part of the eye that adjusts the pupil's diameter, widening it in dim light and narrowing it in bright light. The cornea and retina have refractive and sensory roles respectively.

Question 32Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

Which of the following is a non-metal that is lustrous and exists as a solid at room temperature?

  1. Iodine Correct answer.
  2. Bromine
  3. Phosphorus
  4. Sulphur

Explanation

Iodine is an exception among non-metals because it forms shiny, lustrous crystals, though it is a non-metal. Sulphur and phosphorus are dull solids, and bromine is a liquid at room temperature.

Question 33Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

A piece of zinc is added to copper sulphate solution. Which change is observed?

  1. The blue colour deepens and zinc dissolves without any deposit
  2. The blue colour fades and a reddish-brown deposit appears on the zinc Correct answer.
  3. No change occurs because zinc is less reactive than copper
  4. A white precipitate forms immediately in the solution

Explanation

Zinc lies above copper in the reactivity series, so it displaces copper from copper sulphate. The blue colour of copper sulphate fades as copper ions are removed, and reddish-brown copper deposits on the zinc.

Question 34Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

Which reaction correctly represents the laboratory preparation of ethanol from ethene?

  1. C2H4 + H2 → C2H5OH in the presence of nickel
  2. C2H4 + O2 → C2H5OH on heating
  3. C2H4 + H2O → C2H5OH in the presence of an acid catalyst Correct answer.
  4. C2H4 + CO2 → C2H5OH under pressure

Explanation

Ethene undergoes addition of water across the double bond in the presence of an acid catalyst to give ethanol. This is a hydration reaction in which no other product is formed.

Question 35Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

Why does ethanol have a higher boiling point than ethane, although both have similar molecular masses?

  1. Ethanol has a larger number of carbon atoms than ethane
  2. Ethanol contains a carbon-carbon double bond
  3. Ethanol molecules form hydrogen bonds through the -OH group Correct answer.
  4. Ethane is a polar molecule while ethanol is non-polar

Explanation

The hydroxyl group of ethanol allows hydrogen bonding between molecules, and extra energy is needed to break these attractions. Ethane has only weak dispersion forces, so it boils at a much lower temperature.

Question 36Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

In a flower, which structure develops into the fruit after fertilisation?

  1. The ovary Correct answer.
  2. The stigma
  3. The ovule
  4. The anther

Explanation

After fertilisation the ovary enlarges and develops into the fruit, while the ovules inside it become the seeds. The stigma and anther are parts of the flower that do not form the fruit.

Question 37Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

Which statement correctly describes the role of the placenta in human pregnancy?

  1. It stores the embryo until the uterus is ready for implantation
  2. It allows exchange of nutrients and oxygen between maternal and fetal blood without mixing the two Correct answer.
  3. It produces the amniotic fluid that surrounds the embryo
  4. It secretes testosterone to maintain the pregnancy

Explanation

The placenta is a disc-like tissue with villi that increase surface area for exchange of glucose, oxygen and waste between mother and fetus. The two blood supplies are separated by thin membranes, so they do not mix directly.

Question 38Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

A wire of resistance 12 ohm is cut into three equal pieces and the three pieces are joined in parallel. What is the resistance of the combination?

  1. 4 ohm
  2. 4/3 ohm Correct answer.
  3. 36 ohm
  4. 12 ohm

Explanation

Each piece has resistance 12/3 = 4 ohm. Three 4 ohm resistors in parallel give 1/R = 3/4, so R = 4/3 ohm, which is less than any single piece.

Question 39Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

An electric bulb draws a current of 0.5 A when connected to a 220 V supply. What is the power consumed by the bulb?

  1. 55 W
  2. 220 W
  3. 110 W Correct answer.
  4. 440 W

Explanation

Power is the product of voltage and current, so P = VI = 220 × 0.5 = 110 W. This is the rate at which the bulb converts electrical energy into light and heat.

Question 40Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

In Fleming's left-hand rule, the forefinger indicates the direction of the magnetic field and the middle finger the current. What does the thumb indicate?

  1. The direction of the force on the conductor Correct answer.
  2. The direction of the magnetic poles
  3. The direction of the induced current
  4. The direction of electron drift

Explanation

Fleming's left-hand rule gives the force experienced by a current-carrying conductor in a magnetic field. The thumb points along the force, while the forefinger and middle finger give field and current directions at right angles.

Question 41Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

Why is soft iron preferred to steel for the core of an electromagnet?

  1. Soft iron is easily magnetised and easily loses its magnetism Correct answer.
  2. Soft iron retains magnetism permanently once magnetised
  3. Soft iron has a much higher resistance than steel
  4. Soft iron is a non-magnetic material

Explanation

An electromagnet must be strong while current flows and lose its magnetism when the current stops, and soft iron does exactly this. Steel retains magnetism, which is useful for permanent magnets but not for electromagnets.

Question 42Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

Which type of muscle is involuntary and found in the walls of the stomach and blood vessels?

  1. Smooth muscle Correct answer.
  2. Cardiac muscle
  3. Skeletal muscle
  4. Striated muscle

Explanation

Smooth muscle is not under conscious control and lines hollow organs such as the stomach and blood vessels. Cardiac muscle is also involuntary but is confined to the heart, while skeletal muscle is voluntary and striated.

Question 43Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

A plant shoot is exposed to light coming from one side only. Which explanation best accounts for its bending towards the light?

  1. Auxin accumulates on the shaded side and stimulates greater elongation there Correct answer.
  2. Auxin accumulates on the lit side and inhibits elongation there
  3. Auxin is destroyed on the shaded side, stopping all growth
  4. Auxin moves into the root and pulls the shoot towards light

Explanation

Auxin redistributes towards the shaded side of the shoot, where it promotes cell elongation. The shaded side therefore grows longer, causing the shoot to bend towards the light.

Question 44Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

Which pair of metals can be stored under kerosene because they react vigorously with air and moisture?

  1. Copper and silver
  2. Gold and platinum
  3. Sodium and potassium Correct answer.
  4. Iron and zinc

Explanation

Sodium and potassium are highly reactive alkali metals that catch fire on exposure to air and react violently with water, so they are kept under kerosene. The other listed metals are much less reactive and can be kept in air.

Question 45Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

Which statement best explains why diamond is extremely hard while graphite is soft and slippery?

  1. Diamond contains free electrons that hold the atoms rigidly
  2. Diamond is an ionic solid while graphite is a covalent solid
  3. Graphite contains strong covalent bonds between its layers
  4. Diamond has a rigid three-dimensional covalent network while graphite has weakly held layers Correct answer.

Explanation

Every carbon atom in diamond is covalently bonded to four others in a continuous three-dimensional network, making it very hard. In graphite, strong bonds exist only within layers, which are held together by weak forces and slide over one another.

Question 46Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

A compound with molecular formula C3H6O gives a silver mirror with Tollens' reagent but does not react with sodium hydrogen carbonate. Which compound is it?

  1. Propanone
  2. Propan-1-ol
  3. Propanal Correct answer.
  4. Propanoic acid

Explanation

A silver mirror with Tollens' reagent shows an aldehyde, and no reaction with sodium hydrogen carbonate rules out a carboxylic acid. Propanal fits both tests, whereas propanone is a ketone and does not reduce Tollens' reagent.

Question 47Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

A woman who is a carrier of an X-linked recessive disorder marries a man who does not have the disorder. What is the probability that a son born to them will be affected?

  1. 1/4
  2. 1/2 Correct answer.
  3. 0
  4. 1

Explanation

A son receives his X chromosome from his mother and a Y from his father. Since the carrier mother has one affected X and one normal X, each son has a 1 in 2 chance of inheriting the affected allele and being affected.

Question 48Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

A 2 ohm resistor and a 3 ohm resistor are connected in series with a 10 V battery. What is the potential difference across the 3 ohm resistor?

  1. 3 V
  2. 10 V
  3. 4 V
  4. 6 V Correct answer.

Explanation

The series current is 10 V divided by 5 ohm, which is 2 A. The potential difference across the 3 ohm resistor is then 2 A × 3 ohm = 6 V, and the remaining 4 V appears across the 2 ohm resistor.

Question 49Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

The magnetic field lines around a long straight current-carrying wire form concentric circles. What happens to the strength of the field at a point when its distance from the wire is doubled?

  1. It becomes one-fourth its original value
  2. It becomes half its original value Correct answer.
  3. It remains unchanged
  4. It becomes double its original value

Explanation

The field due to a long straight conductor is inversely proportional to the distance from the wire. Doubling the distance therefore halves the field strength, while the direction still follows the right-hand thumb rule.

Question 50Science (class-level curriculum topics such as metals & non-metals, carbon and its compounds, reproduction, electricity, magnetic effects, control and coordination)

Which sequence correctly describes the events that occur when a nerve impulse reaches the end of one neuron?

  1. An electrical spark jumps directly across the gap between the two neurons
  2. The dendrites of the next neuron generate a hormone that carries the signal
  3. The impulse travels backwards along the same axon to the cell body
  4. A chemical neurotransmitter is released into the synapse and diffuses to the next neuron Correct answer.

Explanation

At a synapse the electrical impulse causes release of a chemical neurotransmitter, which diffuses across the gap and triggers a new impulse in the next neuron. Transmission across the synapse is therefore chemical rather than a direct electrical spark.