Class 10 Science MCQ Questions

When a magnesium ribbon burns in air, it forms a white powder. What is this powder?

• Magnesium hydroxide
• Magnesium carbonate
• Magnesium oxide
• Magnesium chloride

Answer: Magnesium oxide. Magnesium combines with oxygen from the air to form magnesium oxide, burning with a dazzling white flame. It is a combination reaction.

What is the pH of a neutral solution such as pure water?

• 14
• 0
• 1
• 7

Answer: 7. On the pH scale, 7 is neutral, values below 7 are acidic and values above 7 are basic. Lower pH means a stronger acid.

What is the chemical formula of baking soda?

• NaHCO3
• Na2CO3
• NaCl
• CaOCl2

Answer: NaHCO3. Baking soda is sodium hydrogencarbonate, NaHCO3. Washing soda is Na2CO3 (with water of crystallisation) and bleaching powder is CaOCl2.

Which non-metal is a good conductor of electricity?

• Graphite
• Sulphur
• Phosphorus
• Iodine

Answer: Graphite. Graphite, a form of carbon, conducts electricity because it has free electrons between its layers. Most other non-metals are poor conductors.

Iron nails placed in copper sulphate solution turn brownish and the blue colour fades. What type of reaction is this?

• Combination reaction
• Displacement reaction
• Decomposition reaction
• Double displacement reaction

Answer: Displacement reaction. Iron is more reactive than copper, so it displaces copper from copper sulphate, forming iron sulphate. The brown coating is copper metal.

Calcium oxide (quicklime) reacts vigorously with water to form slaked lime and releases a lot of heat. This reaction is:

• Displacement and exothermic
• Decomposition and endothermic
• Combination and exothermic
• Combination and endothermic

Answer: Combination and exothermic. Two substances combine to form one product, calcium hydroxide, and heat is given out. Slaked lime is used for whitewashing walls.

White silver chloride turns grey when kept in sunlight. This is an example of:

• Decomposition caused by heat
• Decomposition caused by light
• Decomposition caused by electricity
• A combination reaction

Answer: Decomposition caused by light. Sunlight breaks silver chloride into silver and chlorine, and the silver makes it grey. This light-sensitive reaction was used in black and white photography.

Fats and oils in food become rancid and smell bad over time. Rancidity is caused by:

• Reduction
• Oxidation
• Neutralisation
• Sublimation

Answer: Oxidation. Oxygen in the air oxidises fats and oils. Chip packets are flushed with nitrogen to slow this down.

A 5 to 8 per cent solution of which acid in water is called vinegar?

• Citric acid
• Methanoic acid
• Ethanoic (acetic) acid
• Hydrochloric acid

Answer: Ethanoic (acetic) acid. Vinegar is a dilute solution of ethanoic acid, used as a preservative in pickles. Pure ethanoic acid freezes in cold weather, so it is called glacial acetic acid.

What is the basic filtering unit of the human kidney called?

• Villus
• Neuron
• Alveolus
• Nephron

Answer: Nephron. Each kidney has a large number of nephrons that filter blood and form urine. Neurons are nerve cells and alveoli are air sacs in the lungs.

Which part of the brain maintains the posture and balance of the body?

• Pons
• Cerebrum
• Medulla
• Cerebellum

Answer: Cerebellum. The cerebellum, part of the hindbrain, controls balance and precise voluntary movements. The medulla controls involuntary actions such as blood pressure and vomiting.

In Mendel's experiment, tall pea plants (TT) were crossed with short ones (tt) and the F1 plants were self-pollinated. What is the ratio of tall to short plants in the F2 generation?

• 1 : 1
• 3 : 1
• 1 : 2 : 1
• 9 : 3 : 3 : 1

Answer: 3 : 1. The F2 plants are TT, Tt and tt in the ratio 1 : 2 : 1, but TT and Tt both look tall, giving 3 tall : 1 short. The 9 : 3 : 3 : 1 ratio comes from crossing two traits.

What is the power of a convex lens of focal length 0.5 m?

• +2 D
• +0.5 D
• +20 D
• +5 D

Answer: +2 D. Power is 1 divided by focal length in metres, so 1 / 0.5 = +2 dioptres. A convex lens has positive power and a concave lens has negative power.

Three resistors of 6 ohm each are connected in parallel. What is their equivalent resistance?

• 3 ohm
• 18 ohm
• 6 ohm
• 2 ohm

Answer: 2 ohm. In parallel, 1/R = 1/6 + 1/6 + 1/6 = 1/2, so R = 2 ohm. In series they would add up to 18 ohm.

In a food chain, roughly what percentage of energy is passed on from one trophic level to the next?

• 10 per cent
• 1 per cent
• 50 per cent
• 90 per cent

Answer: 10 per cent. Only about 10 per cent of the energy is passed on; the rest is used for life processes or lost as heat. This is why food chains usually have only three or four steps.