JEE Main 2014 · 6 Apr · Shift 1, Physics question 27

Hydrogen $\left({}_1\mathrm H^1\right)$, Deuterium $\left({}_1\mathrm H^2\right)$, singly ionised Helium $\left({}_2\mathrm{He}^4\right)^+$ and doubly ionised lithium $\left({}_3\mathrm{Li}^6\right)^{++}$ all have one electron around the nucleus. Consider an electron transition from $n=2$ to $n=1$. If the wave lengths of emitted radiation are $\lambda_1$, $\lambda_2$, $\lambda_3$ and $\lambda_4$ respectively then approximately which one of the following is correct ?