During electrolysis, `O_(2)(g)` is evolved at anode in

Options

A. dil . `H_(2)SO_(4)` with pt electrode
B. aqueous `AgNo_(3)` with pt electrode
C. dil. `H_(2)SO_(4)` with Cu electrode
D. fused `NaOH` with Fe cathod and Ni anode

Explanation

To determine in which scenario oxygen gas (O₂) is evolved at the anode during electrolysis, we need to analyze the reactions and electrode potentials involved. Here’s a step-by-step solution:

### Step 1: Identify the Reactions
During electrolysis, oxygen gas is typically evolved at the anode when water or certain oxidizing agents are present. The common reactions that lead to the evolution of O₂ include:
- The oxidation of water:
\[ 2H_2O \rightarrow O_2 + 4H^+ + 4e^- \]
- The oxidation of hydrogen peroxide (H₂O₂):
\[ 2H_2O_2 \rightarrow 2O_2 + 2H_2O + 2e^- \]

### Step 2: Check Electrode Potentials
To determine whether O₂ will be evolved at a specific electrode, we must look at the standard electrode potentials (E°) of the reactions involved.

- The standard electrode potential for the reaction converting H₂O to O₂ is approximately -1.23 V.
- The standard electrode potential for the copper (Cu²⁺/Cu) couple is about -0.34 V.
- The standard electrode potential for the nickel (Ni²⁺/Ni) couple is about -0.25 V.

### Step 3: Compare Electrode Potentials
The more negative the electrode potential, the less favorable the reaction is for oxidation. Thus, we can compare the potentials:

- For H₂O to O₂: E° = -1.23 V
- For Cu²⁺ to Cu: E° = -0.34 V
- For Ni²⁺ to Ni: E° = -0.25 V

Since -1.23 V (for water) is more negative than both -0.34 V (copper) and -0.25 V (nickel), it indicates that the oxidation of water to oxygen is less favorable than the reduction of copper or nickel ions.

### Step 4: Determine the Correct Options
From the analysis, we conclude:
- Oxygen gas will not be evolved at copper or nickel electrodes because their reduction potentials are higher (less negative) than that of water.
- Therefore, the scenarios where O₂ is evolved at the anode must involve either pure water or H₂O₂, which can be oxidized to produce O₂.

### Conclusion
The correct options for the scenarios where O₂ is evolved at the anode during electrolysis are:
1. Electrolysis of water (not explicitly mentioned but implied).
2. Electrolysis of hydrogen peroxide (H₂O₂).

### Final Answer
O₂ gas is evolved at the anode in:
- Electrolysis of water.
- Electrolysis of hydrogen peroxide (H₂O₂).