Subscripts in a molecular indicate how many of each type of can be found in that molecule.

A subscript is used only when more than one atom of a given type is present.

Explanation:

Molecular formulas are written with an index in the lower right corner. The index indicates the total number of atoms of one chemical element that is part of a molecule.

In the molecular formula of a compound, the coefficients can be different and that means that we have a different number of molecules of the same compound, but the indices cannot be different, because then it is no longer the same compound.

i think its both a and b

the answer is definitely a