The correct statement(s) regarding the binary transition metal carbonyl compounds is (are)
(Atomic numbers : Fe = 26, Ni = 28)
(A) Total number of valence shell electrons at metal centre in Fe(CO)5 or Ni(CO)4 is 16
(B) These are predominantly low spin in nature
(C) Metal - carbon bond strengthens when the oxidation state of the metal is lowered
(D) The carbonyl C–O bond weakens when the oxidation state of the metal is increased