question 17\nwhich of the transitions in the hydrogen atom energy - level diagram shown here is not…

Explanation:

Step1: Recall selection rules

In a hydrogen - atom, electronic transitions occur between energy levels. The selection rule for electric - dipole transitions is $\Delta l=\pm1$. When considering transitions between principal quantum numbers $n$, all of the upward transitions from $n = 1$ to higher $n$ values shown (a: $n = 1\rightarrow n = 5$, b: $n = 1\rightarrow n = 2$, c: $n = 1\rightarrow n = 3$, d: $n = 1\rightarrow n = 3$) are allowed electric - dipole transitions as long as the angular - momentum change rule is followed. In the context of hydrogen - atom energy - level transitions, all the transitions shown in the diagram are possible electric - dipole transitions as they represent absorption of photons to move an electron from a lower to a higher energy level.

Answer:

None of the above (since all transitions a, b, c, d are possible)