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.

Correct Answer: (b) The amount of air available to a person is less than that available on the ground.

Explanation:

Mountaineers climbing high mountains carry an oxygen cylinder along with them because, with increasing altitude, the amount of oxygen in the air decreases. Thus, mountaineers also suffer from dizziness at higher altitudes.
 

The majority of each breath we take consists of nitrogen (79.04%) and oxygen (20.93%). This air composition is stable at both sea level and altitude. Altitude alters the "partial pressure" of oxygen in the air (how many molecules exist in a particular volume). At sea level, oxygen partial pressure is 159 mmHg; at 8,848 m (Mt. Everest), it's 53 mmHg.

At high altitudes, less pressure "pushes" oxygen molecules together. This implies we inhale less oxygen with each breath. Studies call this "hypoxia."

Within seconds of exposure to altitude, ventilation increases as the body adapt to less oxygen and tries to enhance oxygen intake. Despite this response, your circulatory system has less oxygen, meaning your muscles have less oxygen. This hinders exercise.

The first few hours of altitude exposure might lead to dehydration. Altitude can raise your metabolism while suppressing your appetite, so you'll need to consume more to maintain energy balance. After several days or weeks at altitude, people's bodies acclimate to the low-oxygen environment (called "acclimation"). The increase in breathing that began in the first few seconds of altitude exposure continues, and hemoglobin levels (the oxygen-carrying protein in our blood) rise along with the ratio of blood vessels to muscle mass.

Despite body adaptations to hypoxia, physical performance at altitude is always worse than at sea level. Very brief and strong movements, such as throwing or hitting a ball, may benefit from the lack of air resistance. Acute altitude sickness affects those who ascend to moderate or high altitudes. Symptoms include headaches, nausea, lethargy, disorientation, and disrupted sleep. These symptoms are more common in people who ascend swiftly to heights exceeding 2,500m, so hikers are encouraged to climb slowly, especially if they've never been to altitude.

Those with the worst symptoms may have a low hypoxic ventilatory response. Some people aren't terrific singers or footballers, and some people's bodies can't handle less oxygen. Disorders that affect the blood's oxygen carrying capacity, such as thalassemia, can increase symptom risk. Altitude exposure history is the strongest predictor of altitude sickness.

Altitude residents have more physical capacity. Sherpas in Nepal are known for their mountaineering skills. High-altitude residents have huge lung capacities and improved oxygen transport efficiency during rest and exercise. These features, whether hereditary or the result of altitude exposure throughout life, give high-altitude inhabitants an edge over lowlanders in hypoxia.