WAEC - Physics (1989 - No. 14)

Water in an open container boils at a lower temperature when heated at the top of a mountain than at sea-level because at the top of a mountain the

relative humidity is higher than at sea-level

rays of the sun adds more heat to the water

temperature is lower than that at sea-level

pressure is lower than that at sea-level

pressure is more than that at sea-level

Refer to Elementary physics, pressure reduces with height.