What is the temperature at which liquid changes into a solid?

Answer 1

That depends entirely on the strength of the internal bonds of a compound or external bonds of pure elements. For example Gold, which is a solid at room temperature, has a very high melting point due to the strong metallic bonds between the different Gold atoms that clump together to form solid gold, whereas water molecules have weaker bonds and therefore have to be highly compressed or exposed to low temperatures in order to form a solid.
The freezing point of the material.

If you want an actual temperature, you're going to need to specify what the material is.

Answer 2

It depends what type of matter it is, as well as, atmospheric pressure.