Question

coal is said to be formed from wood of trees. why then is considered to be a non renewable source of energy whereas wood is renewable source of energy

Answer 1

coal is considered as a non-renewable source of energy because it takes millions of years to form and they were formed by the buried remains of plants and animals which remained millions of years ago.
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Answer 2

Because the process of formation of wood to coal is very slow, it takes million of years.... That is the reason coal is a non renewable source