Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): Alcohol rather than mercury is used in a thermometer to measure a temperature of −60°C.
Reason (R): Alcohol has a lower freezing point than mercury.
In the light of the above statements, choose the most appropriate answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Both (A) and (R) are correct and (R) is the correct explanation of (A)
Assertion (A): Alcohol rather than mercury is used in a thermometer to measure a temperature of −60°C. True. Mercury becomes solid at about −39°C, so at −60°C it could not move along the tube. Alcohol stays liquid, so alcohol thermometers are used in very cold places.
Reason (R): Alcohol has a lower freezing point than mercury. True. Alcohol (ethanol) freezes at about −114°C, far below the −39°C of mercury.
The Reason explains the Assertion: the liquid in a thermometer must stay liquid at the temperature being measured, and only alcohol, with its lower freezing point, does so at −60°C.