Q 12-12-019NEETJEE MainMedium
In a sample of hydrogen atoms excited to $n = 5$, the number of different spectral lines that can be emitted is
Answer: (D) $10$
Concept. In a sample, atoms in level $n$ can fall by every possible route, giving $\dfrac{n(n - 1)}{2}$ different lines.
Step 1. Substitute $n = 5$.
$$\frac{5 \times 4}{2} = 10$$
Answer. $10$ (Option D).
Solution by Sreeraj P, M.Sc Physics