Which of the following do water, rust, and salt have in common?

The correct answer is Option D.

Explanation:

Atoms are defined as the smallest unit which cannot be further divided.

Mixtures are defined as the solution win which components are mixed in indefinite proportions. Every substance retain their individual chemical properties.

Elements are defined as the substances which are made from only one type of atoms. Example: Sodium (Na), Oxygen (O), etc...

Compounds are defined as the substances which are made from two or more than two types of atoms in a fixed ratio by their mass. For Example:   etc..

We are given:

Three substances having chemical formulas of

All the substances are made from two types of atoms. Thus, they are all considered as compounds.

Hence, the correct answer is Option D.