If a camper in the mountains determines that water in his cooking pot boils at 90°c, then what is the elevation of his campsite?

The elevation of his campsite is 10000 feet.

Explanation:

Boiling point is determined by the elevation from the sea level. At high altitude areas the boiling point of water is low which naturally increases the cooking time of food when methods like boiling and simmering is used.

With an increase of 500 feet from the sea level the boiling point of water decreases by 0.5°C or approximately 1°F. In this question the boiling point is given to be 90°C.

The difference in the boiling point at sea level and this boiling point is

100-90=10°C

With every 1000 feet rise there is a decrease of boiling point by 1°C. Hence the elevation rise

Thus the value of elevation of a location where boiling point of water is 90°C is 10000 feet.

it's all four options.