Sorption is a phenomenon in which one substance becomes attached to another surface. This can occur either by attracting substance into bulk (absorption)or the substance may get attached simply on the surface(adsorption).So (iii) is correct.

‘Absorption’ refers the enter of a substance into bulk phase only. So option (i) is wrong.

Similarly, in ‘Adsorption’ a substance gets adhered to a surface of the adsorbent. So option (ii) is also wrong.

The term ‘Desorption’ means the opposite process of sorption. Therefore, (iv) is an incorrect option.