Find the number of unpaired electrons for copper in ground state configuration.

The total number of magnetic quantum numbers for a $d$-orbital is given by

The quantum number which explains the line spectra observed as doublets in the case of hydrogen and alkali metals, and doublets and triplets in the case of alkaline earth metals is:

The number of angular and radial nodes of $4d$ orbital respectively are

The number of $d-$ electrons in $Fe^{2+}$ (at. no. of $Fe = 26$) is not equal to that of the

Two electrons occupying the same orbital are distinguished by