When a specie undergoes oxidation, its

Analysis of the Question

This question tests your understanding of the fundamental definitions in redox (reduction-oxidation) reactions. You are asked to identify what happens to the oxidation number of a chemical species when it undergoes oxidation.

Concept Explanation

In chemistry, redox reactions involve the transfer of electrons. We use the mnemonic OIL RIG to remember the definitions:

• Oxidation Is Loss (of electrons)
• Reduction Is Gain (of electrons)

When an atom or ion loses electrons, it becomes more positive (or less negative). Because electrons carry a negative charge, losing them causes the oxidation number of the species to increase. Conversely, when a species gains electrons (reduction), its oxidation number decreases.

Step-by-Step Solution

1. Define Oxidation: Oxidation is the process where a species loses electrons.
2. Analyze the effect on charge: Since electrons are negatively charged, removing them from a species makes the overall charge of that species more positive.
3. Relate to Oxidation Number: The oxidation number is essentially the charge an atom would have if all bonds were ionic. Therefore, if a species loses electrons, its oxidation number must shift in the positive direction (increase). • Example: In the reaction $Zn \rightarrow Zn^{2+} + 2e^-$, the oxidation number of Zinc increases from $0$ to $+2$. This is oxidation.
4. Evaluate the Options: • A: Oxidation number increases (Correct, as explained above). • B: Oxidation number decreases (This describes reduction). • C: Oxidation number remains constant (This describes a non-redox reaction). • D: Acts as an oxidizing agent (Incorrect; a species that undergoes oxidation is actually the reducing agent).

Conclusion

Exam Tip

Always remember the "Number Line Rule":

• If the oxidation number moves to the right (e.g., $-2$ to $0$, or $+1$ to $+3$), it is Oxidation.
• If the oxidation number moves to the left (e.g., $+2$ to $0$, or $0$ to $-1$), it is Reduction.