The boiling point of water is:
a.) 0°C
b.) 100°C
c.) -0°C
d.) -100°C

Hint: The temperature at which the vapour pressure of a liquid is equal to the atmospheric pressure is called boiling point. It is surrounding dependent.

Complete step by step answer:
The boiling point of a liquid is the temperature at which the vapor pressure of the liquid equals the pressure of the atmosphere (atmospheric pressure) and the liquid changes into a vapour.
The boiling point of a liquid varies depending upon the surrounding environmental pressure. A liquid at high pressure has a higher boiling point than the same liquid at atmospheric pressure. A liquid in vacuum has a lower boiling point than when that liquid is at atmospheric pressure.
At sea level, the boiling point of water is 100°C. At some higher altitude, the boiling point of water decreases.
The normal boiling point (also called the atmospheric boiling point) of a liquid is different from the boiling point of a liquid. The normal boiling point is defined as the temperature at which the vapour pressure of the liquid is equal to the defined atmospheric pressure at sea level, i.e. one atmosphere. On the other hand, the standard boiling point has been defined by IUPAC since 1982 as the temperature at which boiling occurs under a pressure of one bar.

Hence, the correct answer is (B) 100°C

Note: Unless the temperature variation isn’t mentioned, a student must tell the normal boiling point of the liquid, i.e. at one atmosphere.