Assertion and Reason Questions and Answers

Answer: A

Correct answer: Both A and R are true and R is the correct explanation of A.

Bats emit ultrasonic pulses and listen for the echoes, building a picture of obstacles and prey from the time each echo takes to return. That echolocation is exactly what lets them fly and hunt in complete darkness. Both are true and R explains A.

Answer: C

Correct answer: A is true but R is false.

Carbon dioxide does turn lime water milky, so A is true. But the milkiness is a precipitate of insoluble calcium carbonate: \[ \mathrm{Ca(OH)_2 + CO_2 \rightarrow CaCO_3 \downarrow + H_2O} \] not any “sullying” of the water. R is false.

Answer: B

Correct answer: Both A and R are true but R is NOT the correct explanation of A.

Both statements are true - vaccines do prevent disease, and children should be vaccinated. But R is a recommendation that follows from A rather than a reason for it; what explains A is that a vaccine primes the immune system to recognise the pathogen. R does not explain A.

Answer: A

Correct answer: Both A and R are true and R is the correct explanation of A.

A democracy is by definition a system in which the people choose those who govern them, so India’s being a democracy is precisely why its citizens elect their own representatives. Both are true and R explains A.

Answer: B

Correct answer: Both A and R are true but R is NOT the correct explanation of A.

Both statements are true, but the neutron’s lack of charge is not what makes the atom neutral. The atom is neutral because it contains equal numbers of protons and electrons, whose opposite charges cancel; the neutrons merely add mass without affecting the balance. R does not explain A.

Answer: C

Correct answer: A is true but R is false.

A leak can indeed be smelt, so A is true. But LPG itself is odourless: a strong-smelling odorant, ethyl mercaptan, is deliberately added in tiny quantities so that leaks give themselves away. R is false as stated.

Answer: C

Correct answer: A is true but R is false.

The earth’s outer core really is molten metal, so A is true. But the heat comes from the decay of radioactive isotopes and the heat left over from the planet’s formation - sunlight warms only the top few metres of the surface. R is false.

Answer: A

Correct answer: Both A and R are true and R is the correct explanation of A.

Haemoglobin, the iron-bearing protein in the red cells, is itself a red pigment, and it is present in such quantity that it gives blood its colour. The reason states exactly the cause. Both are true and R explains A.

Answer: B

Correct answer: Both A and R are true but R is NOT the correct explanation of A.

Both statements are true, but the reason is too loose to be the explanation. What spoils washing is specifically the calcium and magnesium ions, which react with soap to form an insoluble scum instead of lather; other dissolved minerals do no such thing. R does not explain A.

Answer: A

Correct answer: R correctly explains A

Watt’s steam engine was developed for one industrial problem above all: pumping water out of flooded mines, which the earlier atmospheric engines did at ruinous cost in fuel. His separate condenser cut that fuel by three-quarters and made the engine practical, so R correctly explains A.