The correct formula for diphosphorus pentafluoride is:

Question

PF, P2F5, P2F6 or K2F5

Answer 1

The answer is in the prefixes:

1. di = 2, so diA means there are 2 A's
2. penta = 5, so pentad means there are 5 B's

you should be able to get the right answer now,

good luck