Peptisation is the process which converts precipitate into colloidal sol when it is shaken with dispersion medium in the presence of a small amount of electrolyte.

Precipitate absorbs one of the ions of the electrolyte and ultimately break into colloidal particles.

So option (iv) is correct.

During coagulation, colloidal particles come together to form large size particles and form precipitate. So (i) is wrong.

Electrolysis brings chemical decomposition by passing electric current through electrolytes. So (ii) is wrong.

Diffusion is a method in which liquid or gas particles move from region of higher concentration to lower concentration. Therefore (iii) is also wrong.