Question

Match List - I with List - II. Match the standard electrode potential of the electrodes at $25^\circ\text{C}$ 

Choose the correct answer from the options given below : 
 

• A. A-II, B-IV, C-I, D-III
• B. A-IV, B-I, C-III, D-II
• C. A-IV, B-III, C-I, D-II
• D. A-III, B-I, C-IV, D-II

Hint:

You do not need to memorize the entire table. Remembering key anchors like $Zn \ (-0.76\text{V})$ and $Cu \ (+0.34\text{V})$ is often enough to quickly eliminate incorrect options in matching questions.

Answer 1

The Correct Option is C

Step 1: Concept:
The question requires matching common transition metal half-cells with their standard reduction potentials ($E^\circ$) at 298 K ($25^\circ\text{C}$).

Step 2: Key Formula or Approach:
Knowledge of the standard electrochemical series is needed. The exact textbook values are:
- $E^\circ(Zn^{2+}/Zn) \approx -0.76 \text{ V}$
- $E^\circ(Cu^{2+}/Cu) \approx +0.34 \text{ V}$
- $E^\circ(Ni^{2+}/Ni) \approx -0.25 \text{ V}$
- $E^\circ(Mn^{2+}/Mn) \approx -1.18 \text{ V}$
We must match these standard values to the closest approximations given in List II.

Step 3: Step-by-step Explanation:

• C. $Zn^{2+/Zn$:} The standard reduction potential is widely known as exactly -0.76 V. This perfectly matches (I). So, C-I.

• B. $Cu^{2+/Cu$:} Copper is one of the few common metals with a positive reduction potential, typically $+0.34 \text{ V}$. The closest value in the list is +0.35 V (III). So, B-III.

• A. $Ni^{2+/Ni$:} The standard value is $-0.25 \text{ V}$. The closest value provided in List II is -0.23 V (IV). So, A-IV.

• D. $Mn^{2+/Mn$:} Manganese is highly electropositive. Its standard reduction potential is $-1.18 \text{ V}$. The closest remaining value in the list is -1.08 V (II). So, D-II.
Bringing it all together: A-IV, B-III, C-I, D-II.

Step 4: Final Answer:
This specific sequence matches option (C).