The correct option is Moles of solute per litre of solution.
Explanation
The concentration of a solution describes the amount of solute present in a given quantity of solvent or solution. Molarity is one of the most common volumetric methods used to express concentration in chemistry.
Detailed Analysis:
- Moles of solute per litre of solution is Correct: Molarity (M) is defined as the number of moles of solute dissolved in one litre (or cubic decimetre) of the solution. It is expressed mathematically as:
Molarity (M) = Moles of Solute / Volume of Solution in Litres
Since it involves volume, Molarity is temperature-dependent, as the volume of a liquid changes with temperature. - Moles of solute per kilogram of solution is Incorrect: There is no standard concentration term defined as moles of solute per kilogram of solution.
- Moles of solute per litre of solvent is Incorrect: Molarity is calculated based on the volume of the entire solution (solute + solvent), not just the volume of the solvent.
- Moles of solute per kilogram of solvent is Incorrect: This defines Molality (m). Molality is the number of moles of solute per kilogram of solvent. Unlike Molarity, Molality is temperature-independent because it is based on mass rather than volume.
Key Takeaway:
Molarity (M) is moles of solute per litre of solution (temperature-dependent), whereas Molality (m) is moles of solute per kilogram of solvent (temperature-independent).