Which one of the following fuels causes minimum environmental pollution?

Answer: (c) Hydrogen

Hydrogen burns to water, with no CO₂, soot or SO₂ (only some NOₓ at high heat).

The idea

A fuel pollutes because of what it contains besides hydrogen: carbon gives carbon dioxide, carbon monoxide and soot; sulphur gives sulphur dioxide; minerals give ash. Rank the fuels by how much of these they have. Hydrogen has none, so it burns to water.

Coal: most carbon, sulphur and ash → Diesel and kerosene: carbon and some sulphur → Natural gas: least carbon among fossil fuels → Hydrogen: no carbon → water and no CO₂ (in air a little NOₓ can form)

Why the others are wrong

(a) Diesel gives soot, NOₓ and SO₂.

(b) Coal is the dirtiest.

(d) Kerosene gives soot and CO₂.

Also know

Hydrogen carries about three times the energy of petrol per kilogram, but it is a very light gas and hard to store and move. In a fuel cell it gives electricity directly. India’s National Green Hydrogen Mission (2023) aims at 5 million tonnes a year by 2030.