Question:
Among the following, the energy of $2 \mathrm{~s}$ orbital is lowest in :
Correct Option: 1
Solution:
As the value of $Z$ (atomic number) increases, energy of orbitals decreases (becomes more -ve value)
$\therefore$ Order of energy of $2 s$ orbital is $\mathrm{H}>\mathrm{Li}>\mathrm{Na}>\mathrm{K}$.