Solution concentration terms:\nThe number of gram-equivalents of solute dissolved per litre of solution defines which concentration unit?

Introduction / Context:
Several concentration units are used in chemistry and process calculations. Selecting the correct unit is essential for stoichiometry, titration, reaction engineering, and quality control. Normality is particularly common in acid-base and redox titrations where equivalents are more convenient than moles.

Given Data / Assumptions:

• Definition required: gram-equivalents of solute per litre of solution.
• Applies to reactions defined by equivalent weight (e.g., H+ or e− transfer).
• Volume basis is the total solution volume.

Concept / Approach:
Normality (N) is defined as equivalents per litre (eq/L). By contrast, molarity (M) is moles per litre, molality (m) is moles per kilogram of solvent, and formality is moles of solute formula units per litre when dissociation is considered. Mole fraction is dimensionless. Thus, the definition given directly maps to normality.

Step-by-Step Solution:

Verification / Alternative check:
Analytical chemistry protocols for titration calculate normality from standardization using equivalents; example: 1 N HCl contains 1 equivalent H+ per litre.

Why Other Options Are Wrong:

• Molarity: uses moles, not equivalents.
• Molality: uses mass of solvent, not volume of solution.
• Formality: similar to molarity but for dissociating solutes; still moles per litre.
• Mole fraction: ratio of moles; dimensionless.

Common Pitfalls:
Using normality interchangeably with molarity; they coincide only when the reaction equivalent equals the mole (e.g., monoprotic acids in simple acid-base reactions).

Final Answer:
Normality.