When water is cooled, it gets converted into ice by a process called P. When ice is warmed, it gets reconverted into the water in a process called Q. Identify P and Q.
The phase transition from liquid to the solid state on cooling or removing heat is called solidification. Conversion of water (liquid) to ice (solid) is an example of solidification.
The phase transition from solid to the liquid state on heating is called melting. Conversion of solid (ice) to water (liquid) is an example of melting.