The gas argon does not take part in chemical reactions. What do you think is its valency?
The valency of the argon gas is zero.
Valency of an element is the number of electrons gained or loosed by that element during a chemical reaction in order to attain a stable electronic configuration. Since argon gas does not take part in any chemical reaction, it indicates that the valence shell of argon gas is already fully filled and thus, its valency is zero.