Answer:
Correct
- Water boils at a temperature below 100°C at higher altitudes
- Water expands on freezing.
- The density of water decreases on freezing.
- Water boils at 100°C under normal pressure
Incorrect
- Water contracts on freezing
- Water boils at a temperature below 100°C in a pressure cooker
Explanation
At higher altitudes, water boils at a temperature lower than 100°C.The atmospheric pressure at higher heights is lower, so the amount of heat required to create the vapor pressure is lower.Water expands as it freezes.This is only possible when it attains 4°C.However, before this temperature, water contracts will decrease in temperature as any other fluid material will behave.Water reaches its maximum density at 4°C.Beyond this temperature, its density reduces as it nears the freezing point.The boiling point of pure water under normal atmospheric pressure is 100°C.Addition of other solute substance will affect this boiling point in that it will increase with some degrees.For example, salt water has a boiling point a bit higher than that of pure water.In a pressure cooker, the water is sealed inside the machine, hence all the heat generated by the process helps in increasing the temperatures inside the cooker.The water thus is super-heated and the boiling point is more than 100°C.
