<u>Answer:</u> The correct answer is compound.
<u>Explanation:</u>
A pure substance is defined as the substance which is formed by same or different type of atoms which are chemically combined in a fixed ratio by mass.
A compound is a substance which is formed by two or more different type of atoms when they chemically combine.
An element is defined as the substance which have only one type of atoms.
Mixture is defined as the solution which is made by the combination of two or more substances in which each substances retain their original chemical properties.
Calcium fluoride is made by the chemical combination of calcium and fluorine atoms. Thus, it is considered as a compound.
Hence, the correct answer is compound.
