Here's why:

* Nonmetals: Bromine (Br) and phosphorus (P) are both nonmetals. Nonmetals generally form covalent bonds, sharing electrons to achieve stability.

* Valency: Bromine has a valency of -1 (it wants to gain one electron) and phosphorus has a valency of -3 (it wants to gain three electrons).

* Compound Formation: To form a neutral compound, the positive and negative charges must balance. The combination of Br5P7 does not result in a balanced charge.

Possible Correct Compounds:

* PBr5 (Phosphorus pentabromide): This is a known compound where phosphorus has a +5 charge and each bromine has a -1 charge.

* PBr3 (Phosphorus tribromide): This is another known compound where phosphorus has a +3 charge and each bromine has a -1 charge.

If you're working with chemical formulas, it's crucial to double-check the accuracy and validity of the compounds.