Question

Which among the following pairs of solutions is isotonic in nature?

• A. \(0.1\) M urea and \(0.1\) M sucrose
• B. \(0.1\) M urea and \(0.1\) M KCl
• C. \(0.1\) M sucrose and \(0.1\) M KCl
• D. \(0.1\) M KCl and \(0.1\) M \(\text{CaCl}_2\)

Hint:

Isotonic solutions have equal osmotic pressure, which depends on the total particle concentration.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Isotonic solutions have the same osmotic pressure at the same temperature. Osmotic pressure depends on the effective number of particles: \(\pi = iCRT\).

Step 2: Find the Particle Concentration:
0.1 M urea: non-electrolyte, \(i=1\), effective 0.1 M.
0.1 M sucrose: non-electrolyte, \(i=1\), effective 0.1 M.
0.1 M KCl: \(i\approx 2\), effective about 0.2 M.
0.1 M \(\text{CaCl}_2\): \(i\approx 3\), effective about 0.3 M.

Step 3: Match the Pairs:
Urea and sucrose both give 0.1 M of particles, so their osmotic pressures are equal. Every other pair has different effective concentrations: urea and KCl (0.1 and 0.2), sucrose and KCl (0.1 and 0.2), KCl and \(\text{CaCl}_2\) (0.2 and 0.3).

Final Answer:
Urea and sucrose at 0.1 M each are isotonic, option (A). \[ \boxed{\text{(A) 0.1 M urea and 0.1 M sucrose}} \]