Answer
a) $1s^{2}$ $2s^{2}$ $2p^{3}$
b) $1s^{2}$ $2s^{2}$ $2p^{6}$ $3s^{2}$
c) $1s^{2}$ $2s^{2}$ $2p^{6}$ $3s^{2}$ $3p^{6}$
d) $1s^{2}$ $2s^{2}$ $2p^{6}$ $3s^{2}$ $3p^{6}$ $3d^{10}$ $4s^{2}$ $4p^{4}$
Work Step by Step
a) Nitrogen has 7 electrons. Therefore according to the Aufbau principal the shells get filled up as- $1s^{2}$ $2s^{2}$ $2p^{3}$.
b) Magnesium has 12 electrons. Accordingly the shells get filled up as- $1s^{2}$ $2s^{2}$ $2p^{6}$ $3s^{2}$.
c) Argon has 18 electrons. Therefore the electronic configuration is- $1s^{2}$ $2s^{2}$ $2p^{6}$ $3s^{2}$ $3p^{6}$.
d) Selenium has 34 electrons. Thus electronic configuration is- $1s^{2}$ $2s^{2}$ $2p^{6}$ $3s^{2}$ $3p^{6}$ $3d^{10}$ $4s^{2}$ $4p^{4}$.
