The correct answer is option4,i.e.Hydrogen. Greenhouse effect -
Gases that trap heat in the earth’s atmosphere are known as Greenhouse Gases.
Greenhouse Gases are Carbon Dioxide, Methane, Nitrous Oxide (N 2O), Water Vapour, and Chlorofluorocarbons.
Greenhouse Gases are capable of trapping the out-going infrared radiation from the earth’s surface thereby causing the Greenhouse effect.
In the above question other than hydrogen gas, rest all the gases have the capability of trapping the heat rays reflecting from the earth. Hence option 4 is correct.