What is a main difference between a mixture and a pure substance? a mixture is only a liquid, but a pure substance can be in any state. a mixture looks the same throughout, but a pure substance does not. a mixture can vary in composition, but a pure substance has a set composition. a mixture can be made up of a single compound, but a pure substance cannot.

The correct answer is option 3: A mixture can vary in composition, but apure substance has a set composition.

Explanation:

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explanation:

covalent bonds

consist of pairs of electrons shared by two atoms, and bind the atoms to fixed orientation and requre high energies to break them

ionic bonds

when two atoms differ considerably in their electronegativity, then one of the atoms will lose its electron to the other atom. this results in a positively charged ion(cation) and a negatively charged ion (anion)