P4Se3
PBr5
Formula: Cs2Se
An empirical formula refers to the chemical formula that indicates the simplest ratio of atoms in a compound. Two different compounds may have the same empirical formula.
A formula unit is an empirical formula.
Almost certainly you are looking for Titanium(IV) Selenide, TiSe2, though the Titanium(III) compound, Ti2Se3 may exist as well. You should be more specific :)
PBr5
Sulfur and phosphorus would most like form the compound P2S5
p2o5
Rubidium selenide has the formula Rb2Se.
Formula: Cs2Se
V2Se5 is the formula for vanadium V selenide.
P underscore 2 O underscore 3
titanium (II) selenide = SeTi
Formula: CdSe
Formula: K2Se
Formula: Se2-
Se2-