Transitions, Photon Emission & Excitation question from MHT CET 2025 (21 Apr, Shift 1)

Answer: (d)

1. Emitted frequency $\nu \propto \left(\frac{1}{n_f^2}-\frac{1}{n_i^2}\right)$; emission needs a jump from higher $n$ to lower $n$.
2. (a) and (b) are absorptions. (c) $5\to3$: $\frac19-\frac1{25} = 0.071$; (d) $2\to1$: $1-\frac14 = 0.75$.
3. So the answer is (d) $n=2$ to $n=1$.