When an aqueous solution of `AgNO_3` is electroysed between platinum electrodes, the substances liberted at anode and cathode are

Options

A. silver is deposited at cathode and `O_2` is liberated at anode
B. silver is deposited at cathode and `H_2` is liberated at anode
C. hydrogen is liberted at cathode and `O_2` is liberated at anode.
D. silver is deposited at cathode and Pt is dissolved in electrolyte.

Explanation

To solve the question regarding the electrolysis of an aqueous solution of `AgNO3` between platinum electrodes, we will analyze the reactions occurring at both the anode and cathode.

### Step-by-Step Solution:

1. **Identify the Electrolyte and Its Components:**
- The electrolyte is `AgNO3`, which dissociates in water to give `Ag^+` (silver ions) and `NO3^-` (nitrate ions).

2. **Determine the Reactions at the Cathode:**
- At the cathode, reduction occurs. The possible cations in the solution are `Ag^+` and `H^+` (from water).
- The standard reduction potentials (E°) for these reactions are:
- For `Ag^+ + e^- → Ag (s)`, E° = +0.80 V (approximately)
- For `2H^+ + 2e^- → H2 (g)`, E° = 0.00 V
- Since `Ag^+` has a higher reduction potential, it will be reduced preferentially.
- Therefore, the reaction at the cathode is:
\[ Ag^+ + e^- \rightarrow Ag (s) \]

3. **Determine the Reactions at the Anode:**
- At the anode, oxidation occurs. The possible anions in the solution are `NO3^-` and `OH^-` (from water).
- The standard oxidation potentials for these reactions are:
- For `2OH^- → O2 (g) + 2H^+ + 4e^-`, E° = -0.40 V (approximately)
- For `NO3^-` oxidation, the potential is generally lower than that of `OH^-`.
- Since `OH^-` has a lower discharge potential, it will be oxidized preferentially.
- Therefore, the reaction at the anode is:
\[ 2OH^- \rightarrow O2 (g) + 2H2O + 4e^- \]

4. **Summarize the Products:**
- At the cathode: Silver (Ag) is deposited.
- At the anode: Oxygen (O2) is liberated.

5. **Conclusion:**
- The substances liberated at the anode and cathode during the electrolysis of `AgNO3` are:
- **Anode:** Oxygen (O2)
- **Cathode:** Silver (Ag)

### Final Answer:
- At the anode, oxygen is liberated, and at the cathode, silver is deposited.