(i) Pressure cooker reduces the cooking time. Explain the priciple involved.
(ii) Fish and meat can be preserved for a longer time in ice if common salt is added to it. Give reason.
(iii) When a glass of ice cold water is kept open at room temperature, what observation is found ? Give reason.

Explanation

(i) In a pressure cooker, water is subjected to heating in a closed vessel in a confirmed space. The steam generated in fixed volume increases the pressure beyond the normal atmospheric pressure. Since the external pressure is more, the boiling point of water rises beyond `100^(@)` C. The temperature of cooking medium being greater than the normal boiling point, therefore, food gets cooked at a faster rate, and thus, saving time and fuel.
(ii) Addition of common salt tpo ice reduces the freezing point of ice to below `0^(@)`C. A mixture of three parts of ice and one part of common salt called freezing mixture can produce a much lower temperature `(-21^(@)`C`)`.Thus, fish and meat can be prevented from spoilage for a longer time in time freezing mixture.
(iii) When a glass of water is kept atr room temperature, water droplets are observed on the outer walls of glass. This is because the water vapour present in air when comes in contact with glass containing ice cold water vapour present in air gets condensed.