Here's why:

* Coefficients indicate the number of molecules or formula units. They tell you how many of each compound or element are involved in a reaction.

* Subscripts are part of the chemical formula itself. They indicate the number of atoms of each element within a single molecule or formula unit.

Example:

The balanced chemical equation for the reaction of hydrogen gas and oxygen gas to produce water is:

2H₂ + O₂ → 2H₂O

* Coefficients: 2, 1, and 2 indicate the number of molecules of each reactant and product.

* Subscripts: 2 in H₂ and H₂O indicate that each hydrogen molecule contains 2 hydrogen atoms, and each water molecule contains 2 hydrogen atoms.

In summary:

* Coefficients: Tell us how many molecules or formula units are involved. They are placed in front of the chemical formula.

* Subscripts: Tell us the number of atoms of each element within a single molecule or formula unit. They are written within the chemical formula.