Solution A, B, C and D are respectively 0.1M Glucose, 0.05M NaCl, 0.05M ${\mathrm{BaCl}}_2$ and 0.1M $\mathrm{A}l{ \mathrm{F}}_3$ Which one of the following pairs is
isotonic ?

The solutions A (0.1 M glucose) and B (0.05 M NaCl) are isotonic. 

They have the same osmotic pressure. The product of molar concentration and the number of ions obtained on the dissociation of 1 molecule of solute is the same for both solutions. Glucose is non-electrolyte and does not dissociate. Hence the product will be, 0.1×0.1 = 0.1 

One molecule of NaCl dissociates to give two ions, 

Hence the product  is 0.05×2 =0.1

Therefore, option C is the right answer