Highway Materials MCQ with answer and solution

Concept

Methane (CH4) is the simplest hydrocarbon. It has the most hydrogen for each carbon atom, so its carbon percentage is the lowest.

Formula

Carbon % in CH4 = 12/16 × 100 = 75%

Step-by-step solution

1. Methane is CH4, with molar mass 12 + 4 = 16. 2. Carbon content = 12/16 × 100 = 75%. 3. Bitumen and asphalt are heavy hydrocarbons with about 80-87% carbon. 4. Tar is also carbon-rich, with about 75-90% carbon and very high free carbon. 5. So methane has the lowest carbon content. Answer is (C).

Explanation

Methane is a light gas with only one carbon atom and four hydrogen atoms. Tar, bitumen and asphalt are heavy, complex hydrocarbons with long carbon chains and rings, so their carbon content is higher. So methane has the lowest carbon content.

Why the other options are wrong

Tar, bitumen and asphalt are heavy hydrocarbons with high carbon content (about 80% or more).

Shortcut

The lighter and simpler the hydrocarbon, the lower its carbon percentage. Methane is the lightest.

Common mistake

Students think a gas has no carbon, or they confuse 'lowest carbon' with 'lowest hydrogen'.