An electron makes a transition from orbit $n=4$ to the orbit n=2 of a hydrogen atom. What is the wave length of the emitted radiation? (R= Rydberg's constant}

Question

$\begin{array}{1 1} \large\frac{16}{4R} \\ \large\frac{16}{5R} \\ \large\frac{16}{2R} \\ \large\frac{16}{3R} \end{array}$