Breathing is more difficult in higher altitudes because the
a. air weighs less
b. partial pressure of atmospheric oxygen is lower
c. partial pressure of atmospheric carbon dioxide is higher
d. partial pressure of atmospheric nitrogen is lower
e. partial pressure of atmospheric oxygen is higher

Option (b).

Explanation:

Breathing may be defined as the inhalation of oxygen and exhalation of carbon dioxide. The breathing depends on the various internal and external factors.

The partial pressure of oxygen is directly proportional to the breathing and the inhalation of oxygen in the body. The altitude contains lower atmospheric pressure and the partial pressure o the oxygen decreases at high altitude. The decrease in the partial pressure of the oxygen reduces the affinity of oxygen with hemoglobin and thus an individual feels difficulty in breathing.

Thus, the correct answer is option (b).