Question

According to the quantum-mechanical model transitions would produce light with the longer wavelength: `2p -> 1s` or `3p -> 1s`?

Answer 1

2p--1s would be the longer wavelength

Explanation:

The lower the energy the longer the wavelength.
The higher the energy the shorter the wavelength.
Blue light has more energy than red light.

dropping from 3p to 1s is a bigger drop than from 2p to 1s.
Therefore the drop from 3p to 1s releases more energy than the drop from 2p to 1s. Because the 3p to 1s has more energy it has a shorter wavelength.

The 2p - 1s has less energy released therefore has a longer wavelength.