Which of the following aqueous solutions should have the highest boiling point?

(i) 1.0 M NaOH(ii) 1.0 M Na2SO4(iii) 1.0 M NH4NO3(iv) 1.0 M KNO3EXPLAIN YOUR CHOSEN ANSWER IN DETAIL.

The boiling point of the aqueous solution depend on the i (van't Hoff Factor)
Boiling point elevation in solution contain above solute
= Kb x molality x  i

i depend on the no. of ions i.e more the no. of ions produced more is the boiling point of the aqueous solution.

Since, 1.0 M  Na₂SO₄ produce maximum no. of ion i.e 2Na⁺ and SO₄^2- (in total three moles ) whereas rest of the three produce only two ions.
Hence correct answer is ii)