Answer the following:

Pure and dry chlorine gas is collected by the upward displacement of air. Give reason.

The gases which are made by chemical reactions are collected in different ways depending on their density. If the gas produced is less dense than the air, then the air goes at the bottom of the test tube since air is denser than gas and the gas occupies space at the top of test tube so downward displacement of air takes place.

On another hand if the gas produced is denser than the air, then the gas occupies space at the bottom of the test tube and air goes at the top of the test tube and, i.e. upward displacement of air takes place.

Since chlorine is denser than air, so it is collected in the test tube or jar by upward displacement of air.