Answer: Tin (Sn)
Explanation: The electron configuration for tin (Sn) is shown in the picture. It's last electrons are:
5s^2 4d^10 5p^2
The valence electrons are in the 5th electron shell and include 2 each in the 5s and 5p orbitals.
so you can see those fluorine atoms have really spread out around the central phosphorus atom. this gives us a trigonal bi-pyramidal molecular geometry for pf5.
Since the exponent is negative, you move the decimal (2.0) to the left two spots leaving you with .02