Identify the correct statement
(A) According to Hund's rule each orbital should be filled with single unpaired electron before pairing
(B) For any orbital,value of "(m)+I" can't exceed its value of "n"
(C) Monovalent cation of any transition element can't have more than "5" unpaired electrons.
(D) `Al^(3+)` has "4" electron having sum of their quantum number "n+m+l=2" .