The boiling point of water varies depending on the pressure above the open surface of water. At standard atmospheric pressure, which is approximately 1 atmosphere or 101.3 kilopascals (kPa), water boils at 100°C (212°F). However, at higher elevations where atmospheric pressure is lower, such as in mountainous regions, the boiling point of water is lower than 100°C. Conversely, in pressurized environments, such as in pressure cookers, the boiling point of water increases above 100°C due to the elevated pressure. This relationship between pressure and boiling point is described by the Clausius-Clapeyron equation, which states that as pressure increases, the boiling point of a liquid also increases, and as pressure decreases, the boiling point decreases. Therefore, the boiling point of water is not always 100°C but depends on the pressure above the open surface of water. Understanding this principle is essential for various applications, including cooking, industrial processes, and the study of atmospheric phenomena such as weather patterns and cloud formation. Hence, the correct answer is [D] Depends on the pressure above the open surface of water.