(a) ${}_{15}\mathrm{P}$ → $1s^2\,2s^2\,2p^6\,3s^2\,3p^3$ Number of unpaired electrons = 3 (b) ${}_{14}\mathrm{Si}$ → $1s^2\,2s^2\,2p^6\,3s^2\,3p^2$ Number of unpaired electrons = 2 (c) ${}_{24}\mathrm{Cr}$ → $1s^2\,2s^2\,2p^6\,3s^2\,3p^6\,3d^5\,4s^1$ Number of unpaired electrons = 6 (d) ${}_{26}\mathrm{Fe}$ → $1s^2\,2s^2\,2p^6\,3s^2\,3p^6\,3d^6\,4s^2$ Number of unpaired electrons = 4 (e) ${}_{36}\mathrm{Kr}$ → $1s^2\,2s^2\,2p^6\,3s^2\,3p^6\,3d^{10}\,4s^2\,4p^6$ Number of unpaired electrons = zero