Which requires the removal of heat, melting or freezing?

Is it evaporation? What is it? Why?

Freezing. If you take away energy from something, (lower its temperature), it will freeze. If you add heat to something, it will melt if it is a solid and evaporate if it is a liquid.

When you add energy to something, the atoms which comprise the substance jiggle and vibrate, meaning that on a large scale, a solid will become a liquid, and a liquid will become a gas.

Freezing, just think about it, the colder it gets the more likely there is going to be snow / hail / ice