Question: Among the following, the energy of $2 \mathrm{~s}$ orbital is lowest in :
$\mathrm{K}$
$\mathrm{Na}$
$\mathrm{Li}$
$\mathrm{H}$
Correct Option: 1
Solution:
In 'K', 2s orbital feel maximum attraction from nucleus (So having less energy) due to more $\mathrm{Z}_{\text {eff }}$.
