Answer: Volume im pretty sure
Well, a compound has a total charge of 0. So, it's electrically neutral. Since the X is 3+ and the Y is 3- they add to 0. Meaning no subscripts are necessary. Why don't you try a different combo?
Like:
A^3 and B^1-, to get a 3- charge you need 3xB^1- so the formula is AB3
Does this help?
Do you have a screen shot or picture of the problem?
Valence electrons are found AT THE OUTERMOST SHELL OF AN ATOM.
Valence electron refers to those electrons that are located furthest away from the nucleus of an atom, that is, they are found at the outermost shell. Valence electrons determine the chemical properties of an element and they are the only ones that get involved in chemical reactions with other elements.