Assuming the compounds to be completely dissociated in aqueous solution, identify the pair of the solutions that can be expected to is isotonic at the same temperature.

Options

A. 0.01 M Urea and 0.01 M NaCl
B. 0.02 M NaCl and 0.01 M `Na_2SO_4`
C. `0.03 M NaCl and 0.02 M MgCl_2`
D. 0.01 M Sucrose and 0.02 M glucose.

Answer

C

Explanation

For isotonic solutions , `pi_1 = pi_2` where, `pi=` Osmotic pressure = iCRT
As the given solutions are at same temperature thus,
`i_(1)C_(1)RT = i_(2)C_(2)RT`
(a) For urea , `i_1 =1,C_1 = 0.01 M`
For `NaCl , i_(2) , C_(2) =0.01 M`
`1 xx 0.01 xx RT ne 2 xx 0.01 xx RT` (not isotonic)
(b) For `NaCl : i_(1) = 2, C_1 =0.02 M`
for `Na_(2)SO_(4) , i_(2) =3, C_(2) =0.01 M `
`2 xx 0.02 xx RT ne 3 xx 0.01 xx RT` (not isotonic)
(c) For NaCl , `i_(1) =2 , C_(1) = 0.03 M `
For Mg`Cl_(2): i_(2) = 3 ,C_(2) = 0.02 M`
`2 xx 0.03 xx RT = 3 xx 0.02 xx RT`
0.06 RT = 0.06 RT
Thus , these solutions are isotonic.