The Brainliest Answer!
Bcoz argon has stable electronic configuration.they neither loose their electrons nor do they gain,and also this has a completely filled outer shell so this doesnt require any more electrons ie.-2 in k-shell,8-in L shell,8in Mshell, so the valency is zero.

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Becoz it is already stable
so it doesn't require more atoms to gain stability
its electronic configuration is 2,8,8, thus satisfies the 3 shells and hence it is the reason for having zero valency.
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