In which of the following ‘d’ subshells are degenerate?

Cu¹⁺ has an electronic configuration of$1{\mathrm{s}}^2 2{\mathrm{s}}^2 2{\mathrm{p}}^6 3{\mathrm{s}}^2 3{\mathrm{p}}^6 3{\mathrm{d}}^{10} 4{\mathrm{s}}^0$. Because the 3d orbital is completely filled, it is degenerate. In all other cases, one or more vacant spaces in the d orbital cause it to be generated.