Answer:
The external atmospheric pressure decreases and so does the boiling point of the liquid.
Step-by-step explanation:
We know that pressure decreases with height. Thus atmospheric pressure decreases at higher elevation.
The implication of this is that, if I take a liquid from sea level to a higher elevation, the external atmospheric pressure on the liquid will decrease and so does its boiling point.
Hence, the liquid boils at a lower temperature when placed at a higher elevation. For this reason, the boiling point of a liquid is lower on the mountain.