Question

Which statement is correct about electron orbitals and energy levels?
A. Yttrium, Y, is the first element in the periodic table with an electron in a f sub-level.
B. The maximum number of electrons in one d orbital is 10.
C. The maximum number of electrons in the 4th main energy level is 18.
D. In a main energy level, the sub-level with the highest energy is labelled f.

The answer is D, but could anyone explain why each statement is wrong/correct?