Which hair cell type is primarily responsible for electromotile (movement) activity that is considered a form of amplification?

Outer hair cell

Explanation:

The hair cell is located in the brain and its responsible for amplification of sound. The hair cell length changes in response to stimulus. For amplification a low input is needed and the surrounding frequency must be close to basila membrane located in the inner hair cell. They can amplify low sound using their hair bubbles. The outer hair cell increase hearing sensitivity and a damage to it brings about low sensitivity.

Also, outer hair cell do not regenerate itself and a damage to it means a permanent damage.