Question

Assertion (A): Methane is lighter than air.

Reason (R): Vapour density of methane is 8 and that of air is 14.4.

Options

• If both A and R are true, and R is the correct explanation of A.

• If both A and R are true, but R is not the correct explanation of A.

• If A is true, but R is false.

• If both A and R are false.

Answer 1

If both A and R are true, and R is the correct explanation of A.

Explanation:

Assertion (A) is true because methane (CH₄) has a lower density than ambient air, causing it to naturally rise. Reason (R) is true and perfectly explains the assertion: using the formula Vapour density = `"Molecular weight"/2`, methane’s vapour density is exactly `16/2` = 8, while the average vapour density of air is approximately `28.8/2` = 14.4. Since methane’s vapour density (8) is significantly lower than that of air (14.4), methane is mathematically proven to be lighter than air.