Answer
Please see the work below.
Work Step by Step
We know that
a. Not allowed because the paired electrons in 2p orbital should have opposite spins.
b. Allowed because electronic configuration is $1s^2 2s^2 2p^4$
c. Not allowed because the electrons in 1s orbital should have opposite spins.
d. Not allowed because 2s orbital can hold at the most two electrons having opposite spins.
