If the amount of gas is decreased and the temperature and pressure stay constant, what will be the effect on its volume?

Volume and number of moles of gas have direct relation.

When the amount of gas increases its volume will increase and when the amount of gas decreases its volume will decrease.

Explanation:

According to Avogadro Law,

Equal volume of all the gases at same temperature and pressure have equal number of molecules.

This law state that volume and number of moles of gas have direct relation.

When the amount of gas increases its volume will increase and when the amount of gas decreases its volume will decrease.

Mathematical relation:

V ∝ n

V/n = K

K is proportionality constant.

When number of moles change from n₁ to n₂ and volume from V₁ to V₂

expression will be,

V₁/n₁ = K     ,     V₂/n₂ = K

V₁/n₁ = V₂/n₂