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