Question

Which of the following pair of solutions is isotonic?
(A) 18 g/L of glucose and 6 g/L of urea solution
(B) 10 g/L of glucose and 10 g/L of urea solution
(C) 0.01 M NaOH and 0.02 M glucose solution
(D) 0.01 M NaCl and 0.01 M glucose solution (NaCl undergoes complete dissociation)

• A. A and B
• B. A and C
• C. B and D
• D. B and C

Hint:

Isotonic condition: \( \pi = iCRT \). For electrolytes, account for dissociation with van’t Hoff factor \( i \).

Answer 1

The Correct Option is B

Two solutions are isotonic if they have the same osmotic pressure: \[ \pi = iCRT \] Let’s analyze:
A) Moles of glucose = \( \frac{18}{180} = 0.1 \, \text{mol/L} \)
Moles of urea = \( \frac{6}{60} = 0.1 \, \text{mol/L} \)
Both are non-electrolytes, so \( i = 1 \) → same \( C \), so isotonic
C)
- NaOH: \( i = 2 \), \( C = 0.01 \) → \( \pi = 2 \cdot 0.01 = 0.02 \)
- Glucose: \( i = 1 \), \( C = 0.02 \) → \( \pi = 1 \cdot 0.02 = 0.02 \)
So, they’re isotonic