Explanation

(b)
Lowering of vapour pressure is a colligative property, i.e., depends only upon the number of particles of solute and not on the nature of solute. $\because$ 0.1 M Glucose $\longrightarrow \$remains undissociated
0.1 m $Ba{Cl}_{4} \rightarrow \ \ Ba^{2 +} + Cl^{-}\ \ \Rightarrow 3\ ions$
0.1 m $MgSO_{4}\ \rightarrow \ Mg^{2 +} + SO_{4}^{2 -}\ \ \Rightarrow 2\ ions$
0.1 M NaCl $\rightarrow Na^{+} + Cl^{-} \Rightarrow 2\ ions$
$\therefore$ 0.1 m $Ba{Cl}_{2}$gives maximum number of particles, hence it exhibits maximum lowering of vapour pressure.