A compound has a fixed melting and boiling point.

Compound:

• Compound may be defined as a pure substance made up of two or elements, chemically combined together in a fixed proportion of mass.
• A chemical compound is formed as a result of the chemical reaction of the constituent elements .
• A chemical compound cannot be formed simply by mixing constituent elements. It is formed only when a chemical reaction takes place between them.
• The properties of a compound are different from those of its constituent elements.
• A compound has a definite molecular formula and fixed melting point and boiling point.
• For example, in water$\left({\mathrm{H}}_2\mathrm{O}\right)$, two elements hydrogen $\left(\mathrm{H}\right)$ and oxygen $\left(\mathrm{O}\right)$ chemically combined together in a fixed proportion of 1:8 by mass.
• Therefore, it has a fixed chemical formula i.e$\left({\mathrm{H}}_2\mathrm{O}\right)$.
• Pure water always freezes at $0°\mathrm{C}\left(273\mathrm{K}\right)$ and boils at$100°\mathrm{C}\left(373\mathrm{K}\right)$.