Question

---- gas is lighter than air.
A. Oxygen
B. Carbon dioxide
C. Hydrogen
D. None of these

Answer 1

Hint: Air is a mixture of gases of Nitrogen, oxygen, carbon dioxide and etc. because the presence of these gases makes the air heavy. These gases increase the air density. The percentage of nitrogen, oxygen on an average is 80 and 20 percent.

Complete step by step answer:
- Air consists of molecular weight of an average of about 29. (Molecular weight of Nitrogen-28 and Molecular weight of oxygen-32).
- Therefore any gas with a molecular weight of less than 29 will be called lighter gases.
- Coming to given options, option A oxygen. The molecular weight of oxygen gas is 32. So, it is heavier than air. So, option A is wrong.
- Coming to option B, Carbon dioxide. The molecular weight of carbon dioxide is 44. So, it is also heavier than air. So, option B is also wrong.
- Coming to option C, Hydrogen. The molecular weight of hydrogen gas 2. So, it is lighter than air because of less molecular weight.
- Therefore hydrogen is the gas lighter than air.

- So, the correct option is C.


Note: Methane and helium are gases lighter than air because the molecular weight of the methane is 16 and the molecular weight of the helium is 4. Air has an average molecular weight of 29. If the molecular weight of any gas is higher than 29 then they are heavier gases.