Consider the following pairs of solution which will be isotonic at the same temperature. The number of pairs of solutions is/are \( \_ \_ \_ \_ \_ \_ \_ \_ \_ \_ \).
A. \( 1 \, \text{M} \) aq. \( \mathrm{NaCl} \) and \( 2 \, \text{M} \) aq. Urea
B. \( 1 \, \text{M} \) aq. \( \mathrm{CaCl}_2 \) and \( 1.5 \, \text{M} \) aq. \( \mathrm{KCl} \)
C. \( 1.5 \, \text{M} \) aq. \( \mathrm{AlCl}_3 \) and \( 2 \, \text{M} \) aq. \( \mathrm{Na}_2\mathrm{SO}_4 \)
D. \( 2.5 \, \text{M} \) aq. \( \mathrm{KCl} \) and \( 1 \, \text{M} \) aq. \( \mathrm{Al}_2(\mathrm{SO}_4)_3 \)