Question

Find the number of spectral lines in Paschen series emitted by atomic hydrogen, when electron excited from ground state to $7^{th}$ energy level, returns back.

• A. 4
• B. 3
• C. 7
• D. 21

Answer 1

Answer: (A)

4

Answer 2

The Paschen series corresponds to transitions ending at the $n=3$ energy level. The electron is excited to the $n=7$ level and de-excites. The possible transitions to $n=3$ from levels $n>3$ are $7 \to 3$, $6 \to 3$, $5 \to 3$, and $4 \to 3$. This gives a total of 4 spectral lines in the Paschen series.