The number of unpaired electrons in gadolinium $(\mathrm{Z} = 64)$ is:

The electronic configuration of gadolinium is,$\left[\mathrm{Xe}\right]4{\mathrm{f}}^{7}5{\mathrm{d}}^{1}6{\mathrm{s}}^2$ and the atomic number of gadolinium is 64.

So number of unpaired electrons is 8.