Describe what happens to the energy of a wave if the frequency decreases

Explanation:

The expression for the relation between the energy of the wave and the frequency is as follows;

Here, E is the energy of the wave, h is Planck's constant and is the frequency of the wave.

It can be concluded from the above expression that the energy of the wave is directly proportional to the frequency of the wave.

If the frequency of the decreases then the energy of the wave decreases but the wavelength of the wave increases as the frequency and the wavelength of the wave has an inverse relationship.

whichever one it is, it's definitely not one that you included on the list you provided.

d. air pressure decreases as altitude increases.