In the context of proposals to the use of hydrogen-enriched CNG (H-CNG) as fuel for buses in public transport, consider the following statements: Which of the statements given above is/are correct?

Answer: (b) 2 and 3 only

Lower CO₂ and hydrocarbons, with up to one-fifth hydrogen.

Statement by statement

1. ✗ WRONG H-CNG reduces CO emissions (by up to ~70%) but does not eliminate them.

2. ✓ CORRECT Less carbon in the fuel mix means less CO₂ and hydrocarbons.

3. ✓ CORRECT Up to 18–20% hydrogen by volume can be blended for buses.

4. ✗ WRONG Hydrogen costs more, so H-CNG is not cheaper than CNG.

The idea

Hydrogen has no carbon. Mixing some of it into CNG means less carbon enters the engine for the same energy, and hydrogen also helps the fuel burn more completely. So carbon monoxide, carbon dioxide and unburnt hydrocarbons all fall. They fall; they do not vanish, because most of the fuel is still methane.

CNG (methane) + about 18% hydrogen → Less carbon per unit of energy → Burns faster and more completely → Less CO, CO₂ and hydrocarbons → But hydrogen is costly → fuel is not cheaper

The trap

“Elimination” is too strong — the word to check.

Elimination technique

Statement 1 says “elimination” of carbon monoxide. Absolute claims usually mark the false statement in Environment PYQs. That removes (a) and (d).

Also know

A blend of about 18% hydrogen by volume needs only small changes in a CNG engine. Delhi ran trial buses on it following a suggestion of the Supreme Court. Nitrogen oxides need watching because the flame is hotter.