Question

why boiling point of liquid increase on increasing the pressure

Answer 1

The boiling point of liquid increases on increasing pressure because they proportional to each other.

Answer 2

According to gay lussac law the pressure of given amount of gas at constant volume is directly proportional to the kelvin temperature.
Hence on increasing pressure we require more temperature to make the liquid boil. Thus increasing the boiling point of liquid.This law is also known as pressure temperature law.