The correct option is D Assertion is incorrect and Reason is correct
The oxidation number of O in O3 is zero.
It can only decrease from zero to -1 or -2 but cannot increase to +2.
Therefore, it can act as an oxidant only.
In SO2, the oxidation number of S is +4.
It can have a minimum oxidation number of -2 and maximum of +6.
Its oxidation number either decreases or increases and hence, it can act both as an oxidising and a reducing agent.