Redox fundamentals: during an oxidation process, which of the following decreases for the species being oxidised?

Introduction / Context:
Redox (reduction–oxidation) reactions are ubiquitous in corrosion, electrochemistry, metabolism, and industrial processes. A clear operational definition avoids confusion when balancing reactions or interpreting half-reactions.

Given Data / Assumptions:

• Oxidation defined as loss of electrons (OIL RIG: Oxidation Is Loss, Reduction Is Gain).
• Oxidation number is a bookkeeping device that typically increases upon oxidation.

Concept / Approach:
When a species is oxidised, it donates electrons; therefore, its electron count decreases. Its oxidation number increases accordingly. The number of ions in solution is not a defining criterion for oxidation; ions may increase, decrease, or remain unchanged depending on the reaction context.

Step-by-Step Solution:

Verification / Alternative check:
Half-reaction examples: Fe^2+ → Fe^3+ + e^− shows one electron lost; oxidation number of Fe increases from +2 to +3 while electrons decrease by 1 for the species.

Why Other Options Are Wrong:

• Oxidation number decreases: opposite of what occurs in oxidation.
• Number of ions: not a universal consequence of oxidation.
• All of these: cannot be true since (b) is false.

Common Pitfalls:
Equating oxidation with oxygen addition only; the electron-transfer definition is more general and applies broadly.

Final Answer:
number of electrons (electron count associated with the species)