The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
Fossil fuel is a general term for buried combustible geologic deposits of organic materials, formed from decayed plants and animals that have been converted to crude oil, coal, natural gas, or heavy oils by exposure to heat and pressure in the earth's crust over hundreds of millions of years. So, coal and petroleum are called fossil fuels as they are formed from the remains of the dead organisms after millions of years. So, the correct option is A which is both assertion and reason are correct and the reason is the correct explanation for the assertion.