Li+ ion being heavily hydrated due to smallest size and hence it's hydrated radius become very large as result has the lowest mobility and Cs+ ion being less hydrated and smallest ionic radius hence has the highest mobility.
The ions in solution are present as hydrated ions. The smaller the size of the ion, the greater the extent of hydration. So the size of hydrated ions becomes larger for smaller sized ion and vice versa.
(1) In tautomerism, an atom changes place but resonance involves a change of position of pi-electrons or unshared electrons.
(2) Tautomers are different compounds and they can be separated by suitable methods but resonating structures cannot be separated as they are imaginary structures of the same compound.
(3) Two tautomers have different functional groups but there is same functional group in all canonical structures of a resonance hybrid.
(4) Two tautomers are in dynamic equilibrium but in resonance only one compound exists.
(5) Resonance in a molecule lowers the energy and thus stabilises a compound and decreases its reactivity. But no such effects occur in tautomerism.
(6) In resonance, bond length of single bond decreases and that of double bond increases e.g. all six C—C bonds in benzene are equal and length is in between the length of a single and a double bond.
(7) Resonance occurs in planar molecule but atoms of tautomers may remain in different planes as well.
(8) Tautomers are indicated by double arrow in between the two isomers but double headed single arrow is put between the canonical (resonating) structures of a resonating molecule.