The correct answer is B. Less than that at sea level.
The boiling point of water is the temperature at which the vapor pressure of the liquid equals the pressure surrounding the liquid and the liquid changes into a vapor. The boiling point of water at sea level is 100 degrees Celsius. However, the boiling point of water decreases as the atmospheric pressure decreases. This is because the vapor pressure of water is inversely proportional to the atmospheric pressure. Therefore, at higher altitudes, where the atmospheric pressure is lower, the boiling point of water is also lower.
For example, at an altitude of 10,000 feet, the boiling point of water is 93 degrees Celsius. This means that if you were to cook food at high altitudes, you would need to cook it for a longer period of time in order to reach the same level of doneness as you would at sea level.
Option A is incorrect because the boiling point of water is not the same at all altitudes. Option C is incorrect because the boiling point of water is not more than that at sea level. Option D is incorrect because the boiling point of water is not equal to the melting point of ice.