When water goes through a phase change, what happens to the temperature of the water? What is the atmospheric greenhouse effect? Name the two most abundant / important greenhouse gases in the atmosphere?

1. Change of the state of water as the temperature is increased or decreased -

As the temperature of water is increased, the liquid state changes to gaseous state. As the temperature of water is decreased, the liquid state changes to solid state.

2.

Greenhouse effect -

It is the process by which the the radiations of the sun get trapped in the atmosphere of the Earth, and increases the temperature of the surface of the planet, and thereby avoiding the situation of the freeing of the Earth's surface.

The two main and important greenhouse gases are - Carbon dioxide, methane, etc.