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People living at sea level have around $5$ million $RBC$ per cubic millimeter of their blood whereas those living at an altitude to $5400$ metres have around $8$ million. This is because at high altitude
people eat more nutritive food, therefore more $RBCs$ are formed
people get pollutionfree air to breath and more oxygen is available
atmospheric $O_2$ level is less and hence more $RBCs$ are needed to absorb the required amount of $O_2$ to survive
there is more $UV$ radiation which enhances $RBC$ production.
Solution
(c) : At high altitudes composition of air remains almost same as at sea level, but density (barometric pressure) of air gradually decreases due to which arterial $pO_2$ is also decreased (hypoxemia). Highaltitudes presents with complex conditions to whichhuman body has to acclimatize. Number of red blood cells per unit volume of blood is likely to be higher in a person living at high altitudes. This is in response to the air being less dense at high altitude. More number of red blood cells are needed to trap $O_2$ from rarefiedair having low $pO_2$ (partial pressure of oxygen).
