Q: Which one of the following pairs of solution will be isotonic at the same temperature ?

(A) 1 M NaCl & 2 M – Urea

(B) 1 M CaCl_{2} & 1.5 M – KCl

(C) 1.5 M AlCl_{3} & 2 M Na_{2}SO_{4}

(D) 2.5 M KCl and 1 M – Al_{2}(SO_{4})_{3}

Solution: For

(A) 1M NaCl solution (i × C_{m}) = 2 × 1M (C_{m} = Molarity)

2M Urea solution (i × C_{m}) = 2M

1M CaCl_{2} solution (i × C_{m}) = 3 × 1M = 3M

1.5 M KCl solution (i × C_{m}) = 2 × 1.5M = 3M

Similarly for 1.5 M AlCl_{3} and 2M Na_{2}SO_{4}

The value of i × C_{m} be 6

and 2.5 M KCl and 1M Al_{2}(SO_{4})_{3} has 5 M each.

So, the each pair of solution

A,B,C and D have same concentration so, all pairs of solution be isotonic,

Answer : A,B,C and D