A nail was gently touched by the hammer and then was hit harder

A nail was gently touched by the hammer and then was hit harder.
(i) When will be the sound created louder?
(ii) Which characteristic of sound here is responsible for change in sound?
(iii) Give the SI unit of loudness.

(i) Sound will be produced when we beat hard on the nails.
(ii) Amplitude of vibrating body is responsible for change in sound.
(iii) The SI unit of loudness is decibel (dB).