Which among the following fuels produces the least amount of soot particles during combustion?

Compressed natural gas is mostly methane and burns very cleanly, releasing the least soot of the fuels listed.

Petrol produces noticeable soot and particulates from partial combustion of its heavier hydrocarbons.

Kerosene burns with a sootier flame owing to its longer carbon chains.

Diesel is notorious for heavy soot and fine particulate emissions.

Cleaner combustion of gaseous fuel leaves little unburnt carbon to form soot.

This is why many cities promote compressed natural gas for public transport to cut particulate pollution.