Question

It is difficult to cook rice in an open vessel by boiling it at high altitudes because of:
A. Low boiling point and high pressure
B. High boiling point and low pressure
C. Low boiling point and low pressure
D. High boiling point and high pressure

Answer 1

Hint: As we move higher in altitude, the atmospheric pressure around us decreases. The variation of boiling point with pressure is not linear.

Complete step by step answer:
The boiling point of a substance is the temperature at which the vapour pressure of a liquid equals the surrounding pressure and the liquid changes into a vapour. The boiling point of a liquid depends on the environmental pressure surrounding it. A liquid in a partial vacuum has a lower boiling point than when that liquid is subjected to some pressure. A liquid at high pressure has a higher boiling point than when that liquid is at atmospheric pressure. Also, a liquid at a pressure lower than the atmospheric pressure has a lower boiling point than when that liquid is at atmospheric pressure. The dependence of boiling point on pressure is not linear. However, in a narrow range of pressures, linear approximation is used.

Also, as we move higher in altitude, the pressure around us decreases. The pressure at any level in the atmosphere may be interpreted as the total weight of the air above a unit area at any altitude. At higher altitudes, there are fewer air molecules above a given surface than a similar surface at lower levels.

Therefore, as we move higher in altitude, pressure decreases and so does the boiling point.

Hence, the correct answer is (C) Low boiling point and low pressure.

Note: Remember that it is difficult to cook at higher altitudes. The low air pressure lowers the boiling point at high altitudes and thus, the water evaporates more quickly.