The longest wavelength in Balmar Series of hydrogen spectrum will be:

The correct answer is Option (4) → 6563 Å

According to Rydberg formula,

$\frac{1}{λ}=R_H\left(\frac{1}{{n_f}^2}-\frac{1}{{n_i}^2}\right)$

$n_f=2,n_i=3$

$\frac{1}{λ}=R_H\left(\frac{1}{4}-\frac{1}{9}\right)$

$⇒λ=6563 Å$