Hydrogen atom emits blue light when it jumps from n = 4 energy level to the n = 2 level. Which colour of light would the atom emit when it changes from the n = 5 level to the n = 2 level?

$\Delta E\propto \left(\frac{1}{n_1^2}-\frac{1}{n_2^2}\right)$

$\text{ Also, }\Delta E\propto \frac{1}{\lambda }$

Since, $\lambda$ is less for transition from n = 5 to n = 2 than for n = 4 to n = 2.

From the given option, only  $\lambda$_Violet < $\lambda$_blue . Thus blue light or violet colour would have been emitted.