An 8% aqueous solution of urea (by mass of solvent) has an elevation in boiling point of x1. 20% aqueous solution of glucose (by mass of solvent) has an elevation in boiling point of x2. If these two solutions are mixed, then the elevation in boiling point is x3.
Then,
Since the van ‘t Hoff factor for both urea and glucose are 1, and elevation in boiling point is a colligative property, it is only dependent on the concentration of solute particles.
Let’s take 1 L of both the solutions and mix it .The concentration of both - urea and glucose will reduce to half of their initial value that is
x12+x22=x3
∴x1+x2=2x3