Question

how is the pitch varied in a.tabla b.violin c.flute

Answer 1

There are parts in every musical instruments that vibrate to produce musical sound. The pitch of the sound produced depends upon the frequency of vibration of the instrument or the air inside a column. Thus, pitch is varied by changing frequency. In tabla vibrating part is the sheet
in flute is the air inside the columns
in violin it is those strings

Answer 2

Sound is produced in a guitar due to vibration of strings caused by plucking them. Sound is produced in a violin due to vibration of strings caused by rubbing them. Sound is produced in a tabla due to vibration of membrane caused by beating it. Sound is produced in a flute due to vibration of air column caused by blowing wind through the holes of the flute.