Question

How does hydration of sodium and potassium play an important role in the selectivity of the potassium channel ?

Answer 1

Selectivity of Na+ channels remain elusive, and these channels aren't as well studied as K+ channels.

Na+ ions pass through voltage gated sodium channels in a hydrated or partially dehydrated state mostly researcher says it is largely argued that sodium ions pass through in a hydrated state), depending on the dimension of the pore.

Can be read at

The permeability of the sodium channel to orga... [J Gen Physiol. 1971]

Potassium ion channels remove the hydration shell from the ion when it enters the selectivity filter.

In brief, sodium can pass a potassium channel. Especially, if potassium is around the channel prefers to take up potassium. The part of the pore so called 'selectivity filterwould be so narrow that only single ions and water molecules can passat a time. this filter has carboxylic groupswhich mimics the oxygen of the potassium ions hydration shell in water. So it would cost a lot of energy to strip of the hydration shell.