This is because in an open system, the lower the pressure the lesser the energy that will be required for boiling point. Lower air pressure results in a lower boiling point.
The is little or no collision of air molecules with the surface of the liquid. But if there is increase in pressure, more energy will be required to get to boiling point because there will be strong collision between air molecules and surface of the liquid.
To know more about boiling point click here:
https://brainly.com/question/25777663
#SPJ4