Sn4+ is the reducing agent because it undergoes oxidation
H2SO3 is the reducing agent because it undergoes oxidation
H2SO3 is the oxidizing agent because it undergoes reduction
Sn4+ is the oxidizing agent because it undergoes oxidation
The oxidation number of sulphur in H2SO3 is +4 and it gets oxidized to +6 in HSO4-. Sn4+ gets reduced to Sn2+ in the given reaction. We can say that H2SO3 is the reducing agent because it undergoes oxidation. Hence, option B is correct.