Amount of air (per unit volume) at high altitudes is less than the amount of air at the surface of the earth.
True
False
The statement is true.
The mountaineers carry oxygen with them because:
(a) At an altitude of more than 5 km there is no air.
(b) The amount of air available to a person is less than that available on the ground.
(c) The temperature of air is higher than that on the ground.
(d) The pressure of air is higher than that on the ground.