Statement (A): Common oxidation number of VIIIA group elements is zero. 

Statement (B): The oxidation number of fluorine is ' −1 'in its compounds. 

Statement (C): The oxidation number of a metal in metal carbonyls is zero.

The combining capacity of VIIIA group elements is zero the reason is zero group elements have stable outer most electronic configuration. 

In fluorine (F), there are seven valence electrons present. To get octet one electron requires to F so that it exhibits −1 oxidation number in its compounds. The electro negativity, EN of fluorine is 4.0. Hence, it gains electrons from others. 

In metal carbonyls, metal have zero oxidation number since the oxidation state of carbonyl group is zero (CO is neutral ligand)