Question

which of the substances depicted here is a pure substance?

Explanation:

A pure substance has only one type of particle. The top - most diagram shows only one type of molecule (each molecule is made up of two different atoms bonded together, but all molecules are identical). The middle diagram has two different types of atoms (different colors), so it is a mixture of elements. The bottom diagram has two different types of molecules (different colors and bonding patterns), so it is a mixture.

Answer:

The top - most substance (the one with only one type of molecule) is a pure substance.