y$)$ which of the following transition are allowed: $5d2s,5p3f,5p3s.$

b$)$ How many electrons can occupy the $6g$ subshell.

c$)$ Write the electronic configuration of $N{i}^{2+}$

d$)$ Give the possible term symbols for carbon $C$:$1s^{2}2s^{2}2p^2$