Electronic configuration of $\mathrm{Cu}$

${ }_{29}\mathrm{Cu}\to 1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^{6}3{\mathrm{d}}^{10}4{\mathrm{s}}^1$

Outermost electron is in 4s sub-shell  $\mathrm{n}=4,\mathrm{l}=0,\mathrm{m}=0,\mathrm{s}=+1/2$ or $-1/2$