Assertion and Reason Questions and Answers

Answer: C

Correct answer: A is true but R is false.

An iron ball does float on mercury and sink in water, so A is true. But the reason is the reverse of what is stated: iron’s specific gravity, about 7.9, is less than mercury’s 13.6 and greater than water’s 1. R is false.

Answer: A

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

Copper has a very low resistivity, second only to silver among common metals, so it carries current with little loss as heat - and it is far cheaper than silver. That low resistance is exactly why it is chosen for wiring. Both are true and R explains A.

Answer: D

Correct answer: A is false but R is true.

Uranium does have a large, unstable nucleus, so R is true. But a heavy unstable nucleus splits: uranium undergoes nuclear fission, not fusion, which is the joining of light nuclei such as hydrogen. A is false.

Answer: A

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

Iron expands when heated, so rails laid tight in cool weather would buckle on a hot day. The gap left between lengths gives the metal room to expand, which is exactly why it is there. Both are true and R explains A.

Answer: A

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

Common salt as sold contains traces of magnesium chloride, which is deliquescent - it absorbs moisture from the air until it dissolves in it. Pure sodium chloride does not do this, so the impurity is exactly the reason for the caking. Both are true and R explains A.

Answer: C

Correct answer: A is true but R is false.

A body immersed in a liquid does weigh less, so A is true. But by Archimedes’ principle the loss equals the weight of the liquid displaced, not any “higher density” of that liquid - which need not be higher at all. R is false.

Answer: D

Correct answer: A is false but R is true.

Baking soda, sodium bicarbonate, is indeed alkaline, so R is true. But that is why it relieves acidity: it neutralises the excess hydrochloric acid in the stomach. It does not create acidity, so A is false.

Answer: A

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

The Himalayan rivers rise in glaciers and snowfields, which melt through the summer and keep the channels flowing even when the monsoon has failed. Peninsular rivers, fed only by rain, dry up. Both are true and R explains A.

Answer: C

Correct answer: Both A and R are false.

Amoebiasis is an infection of the intestine caused by the protozoan Entamoeba histolytica, spread through contaminated food and water - it is not tied to any occupation. Inhaled asbestos dust causes asbestosis, a quite different disease. Both A and R are false.

Answer: A

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

Plaster of Paris takes up water and sets within minutes into a hard mass of gypsum. That is precisely why a bandage soaked in it can be moulded round a limb and left to harden, holding the broken bone still. Both are true and R explains A.