Question

what does a chemical formula show you?
the elements involved in a chemical reaction using the symbols of the elements that make up the substances
the elements on the periodic table that are organized by increasing atomic number from left to right
the elements involved in lifesaving treatments from earlier in history to present modern day medicine
the elements order of reactivity in an equation to determine which element has to be added first

Explanation:

A chemical formula uses element symbols to show the elements that make up a substance. It is not about the organization of elements on the periodic - table by atomic number, elements in lifesaving treatments, or the order of reactivity in an equation.

Answer:

the elements involved in a chemical reaction using the symbols of the elements that make up the substances