Question

Which one of the following gases is lighter than air?
A. Carbon dioxide
B. Chlorine
C. Oxygen
D. Hydrogen

Answer 1

We should know the atomic mass of the given compounds in the options. Calculate the atomic mass of the gases given in the options. The air contains 78 % of the nitrogen. The molecular weight of the nitrogen is 28. The gas which contains less molecular weight then nitrogen should be considered as lighter gas.

Complete Solution :
- In the question it is given which gas is lighter than air among the given options.
- We have to calculate the molecular weight of all the gases given in the options to know about lighter gas than air.
- Coming to option A, Carbon dioxide. The molecular weight of the carbon dioxide is 44. The molecular weight of the carbon dioxide is more than the molecular weight of the nitrogen. So option A is wrong.
- Coming to option B, Chlorine. The molecular weight of the chlorine molecule is 71. The molecular weight of the chlorine is more than the molecular weight of the nitrogen. So option B is wrong.
- Coming to option C, Oxygen. The molecular weight of the oxygen molecule is 32. The molecular weight of the oxygen is more than the molecular weight of the nitrogen. So option C is wrong.
- Coming to option D, The molecular weight of the Hydrogen molecule is 2. The molecular weight of the hydrogen is less than the molecular weight of the nitrogen.
- Therefore hydrogen gas is the lighter gas than the air.
So, the correct answer is “Option D”.

Note: We should calculate the molecular weight of the compounds to know whether they are lighter than the air or heavier than the air. The molecular weight of some elements is as follows.
Atomic weight of the hydrogen is 1.
Atomic weight of the oxygen is 16.
Atomic weight of the carbon is 12.
Atomic weight of the chlorine is 35.5.
Atomic weight of nitrogen is 14.