Question

how is frequency of sound varied in string, wind and percussion instruments?

Answer 1

There are parts in every musical instruments that vibrate to produce musical sound. A tabla has membrane that vibrates and produce sound when hit, a flute has air column to produce sound when air is blown, a guitar has strings that vibrate to produce sound when stuck, etc.

The pitch of the sound produced depends upon the frequency of vibration of the instrument or the air inside a column.