Question

(i) which property of sound wave determines : (a) loudness (b) pitch

Answer 1

amplitude determines loudness
frequency determines pitch

Answer 2

$\small\tt\purple{(a)\: Amplitude:-}$ The loudness of the sound and its amplitude is directly related to each other. Larger the amplitude louder is the sound.

$\small\tt\purple{(b)\: Frequency:-}$ The pitch of the sound and its frequency is directly related to each other. If the pitch is high then the frequency of sound is also high.