0.2 M aqueous solution of glucose solution is isotonic with 0.5% (w/v) solution of solute(S). What is the molecular mass of S in g/mol ?

Isotonic solutions have same molarity
Let molar mass of solute S = M
Concentration = 0.5 g solute in 100 ml solution  
= 5 g solute in 1000 ml solution
$=\frac{5}{M}molesSin1Lsolution$
$Molarity=\frac{5}{M}=0.2\left(Given\right)$
$\Rightarrow M=25g/mol$