The oxidation number of Gold metal is -

Oxidation no .of metal is 1

The electronic configuration of $\mathrm{A}\mathrm{u}$ is $\left[\mathrm{Xe}\right]4{\mathrm{f}}^{14}5{\mathrm{d}}^{10}6{\mathrm{s}}^1$. After removing the 6s¹ electron and gaining +1 charge, $\mathrm{A}\mathrm{u}$ should have noble gas configuration and hence this should be the most stable configuration.