Here's why:

* Chemical Formula: A chemical formula uses symbols and subscripts to represent the elements and their respective quantities in a compound. For example:

* H₂O: This formula tells us that a water molecule contains two hydrogen atoms (H) and one oxygen atom (O).

* CO₂: This formula indicates that a carbon dioxide molecule has one carbon atom (C) and two oxygen atoms (O).

Key Points:

* Smallest Representative Unit: This refers to the simplest unit of a substance that still retains its chemical properties. For molecular compounds, this is a molecule. For ionic compounds, it's a formula unit.

* Number and Type of Atoms: The chemical formula provides this information directly. The subscripts indicate the number of each type of atom present.

* Other Options:

* Chemical Equation: Describes a chemical reaction but doesn't necessarily show the composition of individual substances.

* Empirical Formula: Shows the simplest whole-number ratio of atoms in a compound, but not the actual number of atoms in a molecule.

* Structural Formula: Shows the arrangement of atoms in a molecule, but doesn't always explicitly show the number of each type of atom.

Let me know if you'd like more examples or have any other questions!