Which of the following gasses is/are lighter than air?1.Hydrogen chloride2.Sulfur dioxide3.HeliumSelect the correct answer from the code given below:

1. A

   1 and 2

   1 and 2. HCl and SO2 are both denser than air.

2. B

   Only 3

   Only 3. Helium is lighter than air. Hydrogen chloride and sulphur dioxide are heavier.

3. C

   2 and 3

   2 and 3. SO2 is heavier than air.

4. D

   Only 1

   Only 1. HCl is heavier than air.

Summary. Official key is (b) only 3. Among the three, only helium is lighter than air. Also note: Air ~29 u — Average molar mass of dry air; He = 4 u — Second-lightest element; balloons; HCl = 36.5 u — Denser; fountain experiment; SO2 = 64 u — Denser; collected by upward displacement of air.