Water contained in a jar at room temperature `(20^(@)C)` is intended to be cooled by method -`I` or method `II` given below:
Method -`I` : By placing ice cubes and allowing it ito float.
Method-`II` : By wrapping ice cubes in a wire mesh and allowing it to sink.
Choose best method(s) to cool the water.

Options

A. Method- `I` from `20^(@)C` to `4^(@)C`
B. Method- `I` from `4^(@)C` to `0^(@)C`
C. Method- `II` from `20^(@)C` to `4^(@)C`
D. Method- `II` from `4^(@)C` to `0^(@)C`

Answer

A, D

Explanation

Initially (above`4^(@)C`), a decreases in temperature , increases the density of water and consequently it descends , replacing the relatively warm water. Convention currents set up in this way demands the location of ice to be on the water surface.
Below `4^(@)C` , a decrease in temperature decreases the water density and as a result it ascends up displacing the relatively warm water, To setup convented currents in this way , the position of ice cubes should be at the bottom.