In redox chemistry, a “reduction” step is accompanied by an increase in which quantity for the species being reduced?

Introduction / Context:
Redox (reduction–oxidation) reactions underpin corrosion control, electrochemistry, metallurgy, and biochemical energy transfer. Correctly identifying oxidation versus reduction is essential for balancing reactions and predicting electron flow.

Given Data / Assumptions:

• Reduction is “gain of electrons.”
• Oxidation number tracks apparent electron ownership.
• We consider the species undergoing reduction.

Concept / Approach:
Reduction increases the electron count associated with a species (it accepts electrons). Consequently, its oxidation number decreases (becomes more negative or less positive). Therefore, the only quantity that increases is the number of electrons; oxidation number does not increase during reduction.

Step-by-Step Solution:
Define: reduction = electron gain.Effect on electron count: increases.Effect on oxidation number: decreases (opposite of option b).Choose (a) as the only correct statement.

Verification / Alternative check:
Example: Fe^3+ + e^- → Fe^2+. Electrons increase by 1 for the iron species; oxidation number drops from +3 to +2.

Why Other Options Are Wrong:
Oxidation number (b) increases only in oxidation, not reduction.Both (a) & (b) is contradictory for reduction.Neither: incorrect since electron count does change.

Common Pitfalls:
Mixing up “OIL RIG” mnemonic (Oxidation Is Loss, Reduction Is Gain of electrons).

Final Answer:
number of electrons