Assertion (A): A person goes to high altitude and experiences 'altitude sickness' with symptoms like breathing difficulty and heart palpitations.

Reason (R): Due to low atmospheric pressure at high altitude, the body does not get sufficient oxygen.

In the light of the above statements, choose the correct answer from the options given below

The correct answer is: Both (A) and (R) are true and (R) is the correct explanation of (A).

Step-by-step Explanation:

1. Analysis of Assertion (A):
When a person travels to high-altitude regions (usually above 8,000 feet or 2,400 meters), their body experiences physiological stress due to the change in environment. This condition is commonly known as altitude sickness or acute mountain sickness (AMS). The typical symptoms of altitude sickness include headache, fatigue, dizziness, nausea, breathing difficulty (dyspnea), and heart palpitations (rapid or irregular heartbeats). Therefore, Assertion (A) is true.

2. Analysis of Reason (R):
As altitude increases, the atmospheric pressure decreases. Although the percentage of oxygen in the air remains constant at about 21%, the lower atmospheric pressure means that the air is less dense. As a result, the partial pressure of oxygen (${\mathrm{pO}}_2$) decreases. This reduced partial pressure decreases the pressure gradient between the alveolar air in the lungs and the blood in the capillaries, making it harder for oxygen to diffuse into the bloodstream. Consequently, the body's tissues do not receive sufficient oxygen (a state of hypoxia). Therefore, Reason (R) is true.

3. Evaluating the Connection between (A) and (R):
The physiological symptoms of altitude sickness, such as breathing difficulty and heart palpitations, are the body's direct compensatory mechanisms to cope with the lack of sufficient oxygen. The heart beats faster (palpitations) to pump blood more quickly, and breathing rate increases (breathing difficulty) to take in more oxygen. Since the low atmospheric pressure at high altitude causes this lack of sufficient oxygen, Reason (R) is the direct physiological cause and correct explanation of the symptoms described in Assertion (A).

Thus, both (A) and (R) are true, and (R) is the correct explanation of (A).