How does methane occur ?

Methane occurs

(i) As the main constituent of natural gas

(ii) In coal mine gas.

(iii) In sewage gas, gobar gas, biogas where it is formed due to the bacterial decomposition of organic matter in the absence of air.

(iv) In coal gas to an extent of about 35%.

(v) In marshy lands where it is formed due to the bacterial decomposition of organic matter held under the stagnant water.