Question

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R
Assertion A: Liquid fuels have higher calorific value than solid fuels.
Reason R: Solid fuels ignite at lower temperature than liquid fuels.
In the light of the above statements, choose the most appropriate answer from the options given below:

• A. Both A and R are correct and R is the correct explanation of A
• B. Both A and R are correct but R is NOT the correct explanation of A
• C. A is correct but R is not correct
• D. A is not correct but R is correct

Hint:

Liquid fuels are generally superior to solid fuels because they are easier to store, have higher heat content per unit mass, and leave virtually no ash. However, they are also more volatile and require more careful handling due to their lower ignition points.

Answer 1

The Correct Option is C

Concept: The calorific value (CV) of a fuel is the total heat energy released during its complete combustion. Ignition temperature is the minimum temperature required for a substance to spontaneously catch fire.

Step 1: Evaluate Assertion A.
Liquid fuels generally have a higher calorific value than solid fuels. This is primarily because liquid fuels (like petroleum products) have higher hydrogen content and lower moisture/ash content compared to most solid fuels (like wood or low-rank coal). For example, petrol has a CV of ~45,000 kJ/kg, while anthracite coal is ~30,000 kJ/kg. Thus, Assertion A is correct.

Step 2: Evaluate Reason R.
Solid fuels generally have a higher ignition temperature than liquid fuels. Liquid fuels vaporize easily, and it is the vapor-air mixture that ignites. Solid fuels require more energy to break down the complex structure (pyrolysis) before the combustible gases ignite. Therefore, Reason R is incorrect.