Question

Which of the following will behave as the best reducing agent? Given \[ \text{Al}^{3+} + 3e^- \rightarrow \text{Al} \quad E^\circ = -1.66 \, \text{V} \] \[ \text{Co}^{3+} + e^- \rightarrow \text{Co}^{2+} \quad E^\circ = 1.81 \, \text{V} \] \[ \text{Fe}^{3+} + e^- \rightarrow \text{Fe}^{2+} \quad E^\circ = 0.77 \, \text{V} \] \[ \text{Cd}^{2+} + 2e^- \rightarrow \text{Cd} \quad E^\circ = -0.4 \, \text{V} \]

• A. Al
• B. Co\(^{2+}\)
• C. Fe\(^{2+}\)
• D. Cd

Hint:

The best reducing agent has the most negative reduction potential.

Answer 1

The Correct Option is A

To determine which of the given species will act as the best reducing agent, we need to analyze the standard reduction potentials (\(E^\circ\)). The species with the most negative reduction potential is most likely to act as the best reducing agent.

The reduction potential values provided are: 

Reaction	\(E^\circ\) (V)
\(\text{Al}^{3+} + 3e^- \rightarrow \text{Al}\)	-1.66
\(\text{Co}^{3+} + e^- \rightarrow \text{Co}^{2+}\)	1.81
\(\text{Fe}^{3+} + e^- \rightarrow \text{Fe}^{2+}\)	0.77
\(\text{Cd}^{2+} + 2e^- \rightarrow \text{Cd}\)	-0.4

A reducing agent is a substance that loses electrons and gets oxidized. Thus, the more negative the standard reduction potential, the stronger the reducing agent. Here are the potentials again, sorted in ascending order:

• \(E^\circ (\text{Al}^{3+}/\text{Al}) = -1.66 \, \text{V}\)
• \(E^\circ (\text{Cd}^{2+}/\text{Cd}) = -0.4 \, \text{V}\)
• \(E^\circ (\text{Fe}^{3+}/\text{Fe}^{2+}) = 0.77 \, \text{V}\)
• \(E^\circ (\text{Co}^{3+}/\text{Co}^{2+}) = 1.81 \, \text{V}\)

From the list above, \(Al\) with a reduction potential of \(-1.66 \, \text{V}\) has the most negative value, making it the best reducing agent among the options given.

Conclusion: The best reducing agent is \(\text{Al}\). Hence, the correct answer is Al.