Question

what is atmosphere? why do mountaineers carry oxygen cylinder with them while climbing high mountains?​

Answer 1

The thick layer of the earth is called atmosphere.

We need oxygen cylinders because when we climb a mountain oxygen decreases.

Answer 2

The atmosphere of Earth is the layer of gases, commonly known as air, that surrounds the planet Earth and is retained by Earth's gravity.

                                                     AND

This decreases the number of oxygen molecules per breath making the person suffocated at high altitudes. Mountaineers carry oxygen cylinder while climbing high mountains to avoid suffocation. As we go higher and higher, at high altitudes, amount of oxygen present in the atmosphere is determined by atmospheric pressure.