Discuss briefly de-mineralisation

Demineralised water is obtained by ion exchange resin by passing it through an anion exchange and cation exchange resin. Those resins have large SO3H and COOH groups.

The water is passed through cation exchanger which removes cations like Na+ and Mg+

Now, this water coming out from cation exchanger is acidic, therefore it is passed through the anionic exchanger which removes anions like OH-, NO3-, etc. by exchanging with OH- ions.

In the end, the H+ and OH- thus produced, combine amongst themselves to produce water

This is demineralisation of water by ion exchange resin.