According to the quantum-mechanical model for the hydrogen atom, which of the following electron transitions would produce light with the longer wavelength: 2p→1s or 3p→1s?

Explanation:

The energy of transition of is greater as compared to as there are more quantum levels which leads to more energy.

Also, considering the expression as:

Where,  

h is Plank's constant having value

c is the speed of light having value

is the wavelength

Wavelength is inversely proportional to Energy. Thus, the transition which has lower energy corresponds to higher wavelength.

Thus, answer -