It is observed that mountaineers carry oxygen at high altitudes. Give reason

Explanation

### Step-by-Step Solution:

1. **Understanding Altitude Effects**: At high altitudes, such as in mountainous regions, the atmospheric pressure is lower than at sea level. This means that the air is less dense.

2. **Oxygen Availability**: With lower air density, the amount of oxygen available in the air decreases. This can lead to a condition known as hypoxia, where the body does not receive enough oxygen.

3. **Breathing Difficulties**: Mountaineers may experience breathing difficulties due to the reduced oxygen levels. This can result in symptoms such as shortness of breath, fatigue, and dizziness.

...