Which of the following fuels has the highest calorific value?

Fires in underground coalmines usually occur due to the:

The calorific value of a fuel is 40000KJ/kg. This fuel is most likely to be:

On a cold winter night, the person sleeping in a room with closed door and windows with a coal fire burning inside may die due to the excessive accumulation of:

Which of the following burns without producing a flame?