Question

The concentration of solute in a solution is 3.5 ppm. By which of the following it may be expressed?

• A. 3.5 g/L
• B. 3.5 mol/L
• C. 3.5 mg/L
• D. 3.5 mol/kg

Hint:

Remember: In aqueous solutions, ppm is numerically equal to mg/L. This shortcut is very useful for environmental chemistry and water analysis problems.

Answer 1

The Correct Option is C

Step 1: Recall definition of ppm.
For dilute aqueous solutions, 1 ppm corresponds to 1 part of solute per $10^6$ parts of solution (by mass). Practically, in water: \[ 1 \, \text{ppm} \equiv 1 \, \text{mg of solute per litre of solution} \]

Step 2: Apply this to the given value.
Given concentration = 3.5 ppm. Therefore, in terms of mg/L: \[ 3.5 \, \text{ppm} = 3.5 \, \text{mg/L} \]

Step 3: Match with options.
Option (C) matches: \(\boxed{3.5 \, \text{mg/L}}\).