Bynari means that the compound is formed by two kind of elements.
You have listed three ions, V 5+, Cl - and O 2-.
Binary ionic compounds are formed by a positive ion and a negative ion, so the possible ionic compound formed by the listed ions are:
1) VCl5, where the number 5 next to Cl is a subscript.
2) V2O5, where the number 2 next to V and the number 5 next to O are subscripts.
Subscripts are used to indicate the number of atoms of each element in the formula.
So, the empirical formula searched are VCl5 and V2O5.
I can give you other examples with more ions.
Ca (2+) and S(2-) => Ca2S2 => CaS
Na(+) and F(-) => NaF
Cs(+) and Br(-) => CsBr
