The correct option is C (ii) > (iii) > (i)
Basic strength∝Ability to donate lone pair of elctrons
In compound (a), the lone pair of electrons of N is involved in resonance and make the compound aromatic in nature. Thus, it became a stable compound. Hence, it has the least basic strength.
In compound (b), the lone pair of electrons on N is localised, it is not involved in resonance so it will be readily available to donate its electrons so it has the highest basic strength among others.
In compound (c), the lone pair of electrons are involved in resonance with benzene ring but it more basic than (a) because here aromaticity is already exist and it not due to the lone pair electrons of N.
Hence, the order of basic strength of the given compound follows
(ii) > (iii) > (i)