Which of the following will act as cathode when connected to standard hydrogen electrode which has `E^(@)` value given as zero ?
(i) `Zn^(2+)//Zn, E^(@)=-0.76V`
(ii) `Cu^(2+)//Cu, E^(@)=+0.34 V`
(iii) `Al^(3+)//Al, E^(@)=-1.66 V`
(iv) `Hg^(2+)//Hg, E^(@)=+0.885 V` (A)(i) and (ii) (B)(ii) and (iv) (C)(i) and (iii) (D)(i), (ii), (iii) and (iv)

Options

A. (i) and (ii)
B. (ii) and (iv)
C. (i) and (iii)
D. (i), (ii), (iii) and (iv)

Explanation

To determine which of the given electrodes will act as a cathode when connected to the standard hydrogen electrode (SHE), we need to analyze the standard electrode potentials (E°) of each electrode. The standard hydrogen electrode has an E° value of 0 V.

### Step-by-Step Solution:

1. **Identify the Standard Electrode Potentials**:
- (i) Zn²⁺/Zn, E° = -0.76 V
- (ii) Cu²⁺/Cu, E° = +0.34 V
- (iii) Al³⁺/Al, E° = -1.66 V
- (iv) Hg²⁺/Hg, E° = +0.885 V

2. **Determine the Cathode**:
- The cathode is the electrode where reduction occurs. For an electrode to act as a cathode when connected to the SHE, it must have a positive standard electrode potential (E° > 0 V).
- Compare the E° values:
- Zn²⁺/Zn: -0.76 V (not a cathode)
- Cu²⁺/Cu: +0.34 V (cathode)
- Al³⁺/Al: -1.66 V (not a cathode)
- Hg²⁺/Hg: +0.885 V (cathode)

3. **List the Cathodes**:
- The electrodes that will act as cathodes are:
- Cu²⁺/Cu (E° = +0.34 V)
- Hg²⁺/Hg (E° = +0.885 V)

4. **Select the Correct Option**:
- The correct option that includes both Cu²⁺/Cu and Hg²⁺/Hg is:
- (B) (ii) and (iv)

### Final Answer:
The answer is (B) (ii) and (iv).