Answer: Option (4)
Explanation: Methane (CH4) is one of the green house gas which is about 0.00017% by volume at present.
With the increasing number of factories and the industries, a noticeable amount of methane has been released to the atmosphere so far, and they have the ability to exist in the atmosphere for about 10-12 years. It can also be reduced when undergoes chemical reaction in the atmosphere.
Hence, the correct option here is (4)