As we move up in the atmosphere, air becomes thin. Because of this mountaineers feel little difficulty in inhaling oxygen. To overcome this problem they carry oxygen cylinders along with them.
They carry Oxygen Cylinders because, as the air becomes thinner as the altitude increases, the level of oxygen also decreases.
at the top of mountain the oxygen is present in very less amount so mountaineers carry oxygen cylinder with them
as we go higher the atmosphere becomes very cloudy and oxygen decreases because of that mountaineers carry oxygen cylinder
Mountaineers carry oxygen cylinders with them because the mountaineers experience problem in breathing due to decrease in density of air.
as altitude increases the air becomes thinner and the level of oxygen starts decreasing , hence mountaineers need oxygen cylinders to allow them to breathe normally