CBSE Class 10 Science 2017 · Paper 531/1 · Question 6

Coal and petroleum are fossil fuels because they were formed from the remains of plants and animals (biomass) buried deep under the earth millions of years ago and slowly changed by heat and pressure. They are not renewable sources of energy because they took millions of years to form and their reserves are limited; they are being used far faster than nature can replace them, so once used up they cannot be renewed, and they will be exhausted however carefully we use them. A greenhouse gas released on their combustion: carbon dioxide, ${\text{CO}}_2$.