Why is Bi(V) a stronger oxidant than Sb(V) ?

Explanation

Due to inert pair effect, the stability of +5 oxisdation states decresase down the group, i.e., +5 oxidation state of Sb is more stable than +5 oxideation state of Bi. Thus, `Bi^(5+)` has a higher tendency to accept a pair of elections than `Sb^(5+)` i.e.,
`Bi^(5+)+2e^(-)toBi^(3+)`, higher tendency to accept electrons , stronger oxidising agent
`Sb^(5+)+2e^(_)toSb^(3+),` lower tendancy to accept electrons , weakder oxidising agent
In other words, Bi (V) is a stronger oxidising agent than Sb (V).