Which one of the following is the main constituent of LPG?

LPG is a mix of hydrocarbon gases that are liquefied under moderate pressure, and its bulk is propane and butane. Between the given options, Butane (C) is the constituent that fits, and it is the key the question expects.

Why the others are wrong:

• Methane (D) is the lightest alkane and the main component of natural gas (CNG/PNG). It does not liquefy at ordinary LPG pressures, so it is not an LPG constituent.
• Pentane (B) and Hexane (A) are heavier and liquid at room temperature. They fall in the petrol and naphtha range of fractional distillation. Hexane is also used as an industrial solvent, such as in edible oil extraction.

The core concept is fractional distillation of crude oil and the C1 to C4 gas fraction. This links to the syllabus on petroleum products and energy, and to the Mains angle of India's import dependence on LPG and the PM Ujjwala Yojana (2016) for clean cooking fuel.

Trap: Candidates pick Methane because it is the most familiar gas. Remember that Methane is natural gas, while LPG is the propane-butane fraction.