An inhabitant of Varanasi goes to Rohtang and experiences nausea, fatigue and heart palpitations. It is because

Options

A. he is experiencing altitude sickness
B. his RBC count is lower than required
C. he is in an area of low atmospheric pressure
D. all of these

Explanation

### Step-by-Step Solution:

1. **Identify the Symptoms**: The inhabitant of Varanasi experiences nausea, fatigue, and heart palpitations after traveling to Rohtang. These symptoms are indicative of a physiological response to a change in environmental conditions.

2. **Understand the Location**: Varanasi is located in the plains of Uttar Pradesh, while Rohtang Pass is situated at a high altitude near Manali, which is significantly higher than 3500 meters above sea level.

3. **Recognize the Condition**: The symptoms mentioned are typical of altitude sickness, which occurs when individuals who are accustomed to lower altitudes suddenly ascend to high altitudes where the air pressure is lower.

4. **Analyze the Cause**: At high altitudes, the atmospheric pressure decreases, which leads to a reduction in the availability of oxygen. The body struggles to obtain sufficient oxygen, resulting in symptoms such as nausea and fatigue.

5. **Physiological Adaptations**: The body begins to acclimatize to high altitude conditions over time. This includes:
- Increasing the production of red blood cells (RBCs) to enhance oxygen transport.
- Increasing the breathing rate to improve oxygen intake.
- Decreasing the affinity of hemoglobin for oxygen, allowing for more efficient oxygen release to tissues.

6. **Conclusion**: The symptoms experienced by the inhabitant of Varanasi are due to altitude sickness caused by low atmospheric pressure and low oxygen availability at high altitudes. Therefore, the correct answer is that all the provided options (low RBC count, low atmospheric pressure, and altitude sickness) contribute to the symptoms experienced.

### Final Answer:
The inhabitant of Varanasi experiences nausea, fatigue, and heart palpitations due to altitude sickness, which is caused by low atmospheric pressure and low RBC count at high altitudes.

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