Changing a subscript in a correctly written chemical formula will change the number of atoms of that element in the molecule.

Here's why:

* Subscripts indicate the number of atoms. For example, in H₂O, the subscript "2" means there are two hydrogen atoms, while the lack of a subscript on "O" means there's one oxygen atom.

* Changing a subscript alters the composition. If you changed H₂O to H₂O₂, you'd be changing the molecule from water to hydrogen peroxide, a completely different substance with different properties.

Important Note:

Changing a subscript does not change the element itself. It only changes the number of that element present in the molecule.