Final answer:
The valency of argon is zero because it has a full valence shell, making it chemically inert and giving it no tendency to form bonds with other elements.
Step-by-step explanation:
The valency of argon is zero. Argon is a noble gas with an electron configuration of [Ne]3s23p6, which means it has a full outer shell of electrons.
A full valence shell gives argon a stable configuration, and because it does not need to gain or lose electrons to achieve stability, it has no tendency to combine with other elements, leading to a valency of zero.
This inertness of argon makes it useful in applications where reactions are not desired, such as in gas-filled electric light bulbs and fluorescent tubes, where it helps in prolonging the life of the bulb and in regulating the temperature.