Answer: option C) pure substance.
Justification:
A sharp melting point is a characteristic of pure substances.
The pure substances are either elements or compounds: they have a unique chemical constitution (kind of elements, number of atoms of each element in the chemical formula, and same chemical bonds).
Other products, this is mixtures (either homogeneus or heterogeneous), being composed of different elements and compounds in different variable ratios, exhibit a range as boiling point. For example the boiling point of the gasoline is about 19°C to 200°C.
Bromine is an element: you find it in the periodic table, with the atomic number 35, hence a pure substance.
