**The boiling point of water at atmospheric pressure**

The boiling point of a substance is the temperature at which it changes from a liquid to a gas. It is the temperature at which the vapor pressure of the substance is equal to the atmospheric pressure. In the case of water, the boiling point depends on the pressure exerted on it.

**Atmospheric pressure and boiling point of water**

Atmospheric pressure is the pressure exerted by the Earth's atmosphere on objects within it. It is commonly measured in units of millimeters of mercury (mmHg), also known as torr, or in pascals (Pa). At sea level, the average atmospheric pressure is around 760 mmHg or 101.3 kilopascals (kPa).

**Boiling point of water at atmospheric pressure**

The boiling point of water at atmospheric pressure is 100°C or 212°F. This is the temperature at which water changes from a liquid to a gas and starts to boil. At this temperature, the vapor pressure of water is equal to the atmospheric pressure. When the atmospheric pressure increases, such as at higher altitudes, the boiling point of water decreases. Conversely, when the atmospheric pressure decreases, such as in a vacuum, the boiling point of water increases.

**Explanation of the correct answer**

Option D, 100°C, is the correct answer because it represents the boiling point of water at atmospheric pressure. At sea level, where the atmospheric pressure is around 760 mmHg or 101.3 kPa, water boils at 100°C. The other options, 95°C, 90°C, and 110°C, do not represent the boiling point of water at atmospheric pressure.