Find the number of unpaired electrons for copper in ground state configuration.
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Copper (Cu) is an exception to the typical electron filling rules. Its ground state electron configuration is $[Ar]3d^{10}4s^1$ rather than $[Ar]3d^94s^2$. This is because a completely filled $d$-subshell ($d^{10}$) provides greater stability, even at the expense of a half-filled $s$-subshell ($s^1$). Always remember the common exceptions for electron configurations, especially for transition metals like Cr and Cu.