Is the amount of energy in a sound wave per unit of time and is also related to the loudness of a sound.

I'm kinda late on telling you the answer but the answer is Intensity. I know it is correct because I had the same question.

The loudness of a sound is related to the amplitude of the waves measured. amplitude is the height of the waves. since energy is proportional to amplitude which means energy increases when the amplitude of the waves are increased, then the amount of energy is related to the loudness of the sound.