Answer:
Only number of electrons of Chlorine and argon are going to be same remaining things like mass,reactivity,ionic radii, and so on will be different so if a chlorine gains a electron we can't call it argon!! chlorine is an diatomic gas, argon exist as monoatomic, chlorine can loose that electron and form bond with another cation in order to remove the charge density,, but argon is stable itself!
