Which pair of solutions is isotonic to each other?

• A. 0.9% NaCl and 10% glucose
• B. 0.9% NaCl and pure water
• C. 0.9% NaCl and 5% glucose
• D. 0.45% NaCl and 5% glucose

Answer: (C)

Verified step by step guidance

1. Understand that isotonic solutions have the same osmotic pressure, meaning they have the same total concentration of solute particles in solution.
2. Calculate the molarity of each solution by converting the given percentage (weight/volume) into moles per liter. For example, for NaCl, use its molar mass (~58.44 g/mol) to find moles from grams, and for glucose, use its molar mass (~180.16 g/mol).
3. Determine the total concentration of solute particles for each solution. Remember that NaCl dissociates into two ions (Na\+ and Cl\-), so its effective particle concentration is twice its molarity, while glucose does not dissociate and contributes one particle per molecule.
4. Compare the total particle concentrations of the pairs of solutions given to see which pairs have approximately equal osmotic pressures, indicating isotonicity.
5. Conclude that the pair with matching total solute particle concentrations (osmolarity) is isotonic, which explains why 0.9% NaCl and 5% glucose are isotonic to each other.