Which concentration unit remains independent of temperature changes: molarity, normality, or molality?

Introduction / Context:
Engineers select concentration units carefully, because temperature changes alter solution volumes and therefore change certain measures of concentration. Picking a temperature-invariant unit simplifies calculations across varying thermal conditions.

Given Data / Assumptions:

• Molarity (mol/L) and normality (equivalents/L) use solution volume in the denominator, which expands or contracts with temperature.
• Molality (mol solute per kg solvent) uses mass, which is independent of temperature.

Concept / Approach:
Because volume is temperature dependent while mass is not, any concentration defined per unit volume changes with temperature. Molality is defined per unit mass of solvent and therefore remains constant when the solution warms or cools (assuming no evaporation or mass loss).

Step-by-Step Solution:
Identify definitions: M = mol/L; N = eq/L; m = mol/kg solvent.Recognize thermal expansion affects L but not kg.Thus only molality is temperature independent.

Verification / Alternative check:
Laboratory practice: standard solutions specified by molarity are prepared at a reference temperature; molal solutions avoid this dependency.

Why Other Options Are Wrong:
Molarity and normality vary with volume changes due to temperature, so they are not invariant.“None of these” is incorrect because molality does meet the criterion.

Common Pitfalls:
Confusing molarity (volume based) with molality (mass based); ignoring solvent evaporation effects in open systems.

Final Answer:
molality