The sounds of different people can easily be identified even without having seen them. Identify the characteristics of the sound wave and the factor on which it depends.

Loudness and wave amplitude

The correct answer is Option (2) → Loudness and wave amplitude

Note: Given answer is as per NTA. However, prima facie the answer appears to be wrong as explained below. The correct answer should be option 4. 

Different people’s voices are identified by the quality (timbre) of sound. Quality depends on the waveform of the sound produced by the vocal cords, not on loudness (amplitude), frequency, or wavelength. Loudness only tells you how much energy the sound has; it doesn't help you tell the difference between Person A and Person B if they are both speaking at the same volume.