Consider the following pairs of solution which will be isotonic at the same temperature. The number of pairs…

A solution having the same solute and solvent concentration as a cell across the semipermeable membrane is referred to as isotonic solution.

The effective concentration of each solution can be calculated as follows,

Effective concentration $=\mathrm{i}({\mathrm{Von}}^{\text{'}}\mathrm{t} \mathrm{Hoff} \mathrm{factor})\times \mathrm{C}$

$1\mathrm{M} \mathrm{NaCl}$ has effective concentration $=2\times 1=2\mathrm{M}$ and hence it is isotonic with two molar urea solution.

$1\mathrm{M} {\mathrm{CaCl}}_2$ has effective concentration $= 3\mathrm{M} \mathrm{and} 1.5\mathrm{M} \mathrm{KCl}$ has also $3\mathrm{M}$, hence, both are isotonic.

$1.5\mathrm{M} {\mathrm{AlCl}}_3\cong 6\mathrm{M} \mathrm{and} 2\mathrm{M} {\mathrm{Na}}_2{\mathrm{SO}}_4\cong 6\mathrm{M}$, Hence both are isotonic.

$2.5\mathrm{M} \mathrm{KCl}\cong 5\mathrm{M} \mathrm{and} 1\mathrm{M} {\mathrm{Al}}_2{\left({\mathrm{SO}}_4\right)}_3\cong 5\mathrm{M}$, Hence both are isotonic.