1. Crystallization. Magma cools either underground or on the surface and hardens into an igneous rock.
2. weathering and erosion
3. This happens due to geologic uplift and the erosion of the rock and soil above them. At the surface, metamorphic rocks will be exposed to weathering processes and may break down into sediment.
4. Rock Melting.
Metamorphic rocks underground melt to become magma. If you need more help https://www.ck12.org/earth-science/rock-cycle-processes/lesson/Rocks-and-Processes-of-the-Rock-Cycle-HS-ES/
This would be the Melting point because it is showing that at a certain heat it melts so therefore it is the point it melts and therefore called the melting point
The most common species of nitrogen in which its oxidation state is zero is the diatomic nitrogen (

). This is because the oxidation number of pure elements (whether alone as an atom or combined with other atoms of the same element such as the diatomic nitrogen) is always zero.
In addition to diatomic nitrogen, there are diazonium (

) compounds where nitrogen has an oxidation number of zero.