NEET 2023 Chemistry Balancing Redox Reactions MCQ Question

To understand how to balance a redox reaction, let’s break down the process step by step, which ultimately leads us to the correct coefficients for the reaction.

Step 1: Identify the Oxidation and Reduction Half-Reactions

In a redox reaction, one species is oxidized (loses electrons) and another is reduced (gains electrons). The first step in balancing a redox reaction is to separate it into its oxidation and reduction half-reactions.

1. Oxidation half-reaction: Identify which species is losing electrons and write the half-reaction for it.
2. Reduction half-reaction: Identify which species is gaining electrons and write the half-reaction for it.

Step 2: Balance Each Half-Reaction

1. Balance the number of atoms of each element involved in the half-reaction.
2. Balance the charges by adding electrons ($e^-$) to the appropriate side.

Step 3: Equalize the Number of Electrons

To combine the half-reactions, ensure that the number of electrons lost in the oxidation half-reaction equals the number of electrons gained in the reduction half-reaction. This may involve multiplying the half-reactions by appropriate coefficients.

Step 4: Combine the Half-Reactions

After balancing and equalizing the electrons, add the two half-reactions together to form the balanced redox equation. Ensure that all species are balanced in terms of both mass and charge.

Example Reaction

Let’s consider a hypothetical example where we have a redox reaction involving reactants and products. For our explanation, let's denote:

• Oxidized species: A
• Reduced species: B

The balanced reaction can be represented as:

$a\,\text{A} + b\,\text{B} \rightarrow c\,\text{C}$

Given Options and Correct Coefficients

From the question, we need to find the coefficients $a$, $b$, and $c$. The correct answer is given as $1$, $8$, and $3$, corresponding to option D.

Explanation of the Correct Answer (1, 8, 3)

When we apply the balancing steps outlined above, we find the coefficients that satisfy both mass and charge balance:

• 1 for the oxidized species (A),
• 8 for the reduced species (B),
• 3 for the product (C).

This means in the overall balanced reaction:

$1\,\text{A} + 8\,\text{B} \rightarrow 3\,\text{C}$

Why Other Options are Incorrect

1. Option A (3, 8, 1):

   • Here, the ratio suggests that you need 3 moles of A for every 8 moles of B, which disrupts the balance because the product C is only 1. This does not satisfy the conservation of mass and charge.

2. Option B (1, 8, 3):

   • This option is a misinterpretation of the correct answer, as it was stated in the instructions that this is not the answer.

3. Option C (8, 1, 3):

   • This suggests that you have 8 moles of A, which would lead to an imbalance in the number of electrons and atoms in the overall reaction when combined.

Conclusion

The correct way to balance the given redox reaction is indeed to have the coefficients $1$, $8$, and $3$ for the respective species involved. Through a systematic approach of identifying half-reactions and balancing them, we've confirmed that the answer is option D (1, 8, 3).

This method not only helps in arriving at the correct coefficients but also reinforces the fundamental concepts of redox reactions and their balance in chemical equations.