Question

Energy of the state $S_1$ in units of the hydrogen atom ground state energy is:

• A. 0.75
• B. 1.5
• C. 2.25
• D. 4.5

Answer 1

The correct option is C 2.25

$S_1$ is spherically symmetrical state, i.e, it corresponds to an s-orbital. Also, it has one radial node.
Number of radial nodes $=n-l-1$
$\Rightarrow n-0-1=1$

Ground state energy of electron in H-atom $\left(E_H\right)$
$E_H=\frac{k{Z}^2}{n^2}=k(Z=1,n=1)$

for $S_1$ state of $L{i}^{2+}$,

$E=\frac{k(3{)}^2}{2^2}=\frac{9}{4}k=2.25k$