Determine how many electrons can be contained in the 5F sublevel.

All of the F's sublevels, including the 5F contains 7 orbitals. Then, each orbital should contain 2 electrons. From the given above, the number of electrons in the sublevel is calculated through,

n = (7 orbitals) x (2 electrons / orbital) = 14 electrons

Thus, the 5F sublevel contains 14 electrons.