$\begin{array}{r}{K}_{19}=1s^2\mathit{,}{25}^2,2p^{6,}3s^2\mathit{,}3p^6\mathit{,}{45}^1\\ \sigma =(7\times 0.35)+(2\times 0.85)+2\times 1\\ =2.45+6.80+2\\ =11.25\end{array}$

$\begin{array}{r}{C}_{20}=1s^{2}2s^{2}2p^6{35}^{2}3p^6\left[4s^2\right]\\ \sigma =(4\times 0.35)+(8\times 0.85)+2x\\ =2.45+6.80+2\\ =\left[11.25\right]\end{array}$