The wavelength will be minimum in the transitions of electrons from

n=2 to n=1

The correct answer is Option (3) → n=2 to n=1

According to photoelectric effect.

$λ=\frac{hc}{ΔE}⇒λ∝\frac{1}{ΔE}$

[ΔE → Energy difference between two levels]

for transition from $n=2$ to $n=1$,

$ΔE=13.6eV\left(\frac{1}{{n_f}^2}-\frac{1}{{n_i}^2}\right)$

$=13.6\left(1-\frac{1}{4}\right)=10.2eV$

Also, the transition from $n=2$ to $n=1$ has the largest potential difference.

and hence, the smallest wavelength.