Atom F has 4 valence electrons. How you can tell this: The 5th electron that is removed requires the greatest amount of energy to remove, since it is removed from an inner electron shell.

Since F has 4 valence electrons, it would need 4 electrons to be donated/shared with it. Hence, each G atom shares 1 valence electron with it, forming a compound comprising of 4 G atoms and 1 F atom.