Statement (A): Oxygen exhibits more than one oxidation states. 

Statement (B): Nitrogen exhibits -1/3 oxidation state

 Statement (C): Sodium exhibits +2 oxidation state

Oxygen exhibits more than one oxidation state in its compounds.

Ex: In peroxides, the oxidation state of oxygen is $-1$  but in super oxides, the oxidation state of oxygen is$-\frac{1}{2}$ . In hydrazoic acid, ${\text{N}}_{\text{3}}\text{H}$ the oxidation state of nitrogen is $-\frac{1}{3}$  because the oxidation state of hydrogen is$\text{+1}$ .Sodium is a group IA element so it exhibits $\text{+1}$  oxidation state only.