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

Statement (A) describes a typical case of altitude sickness: when a person ascends to a high altitude, they often experience difficulty in breathing (dyspnea), rapid breathing, and heart palpitations. These symptoms are well‑documented in physiology and medicine.

Statement (R) explains the physiological cause of these symptoms. At high altitude the atmospheric pressure is lower, which means the partial pressure of oxygen in the air is reduced. Because the driving force for oxygen to diffuse from the lungs into the bloodstream is lower, the body receives less oxygen (hypoxia). The body responds by increasing breathing rate and heart rate to deliver more oxygen to tissues, which manifests as the symptoms mentioned in (A).

Since both statements are factually correct and the low‑pressure‑induced oxygen deficiency directly accounts for the breathing difficulty and heart palpitations, statement (R) serves as the correct explanation for statement (A). Therefore the appropriate choice is that both (A) and (R) are true and (R) explains (A).