Assertion`(A): ` The rusting on the surface of iron involves following reaction `:`
`a. Fe(s) rarr Fe^(2+)(aq)+2e^(-)`
`(` at anodic site `)`
`b. O_(2)(g) +4H^(o+)(aq)+4e^(-) rarr 2H_(2)O(l)`
`(` at cathodic site `)`
`c. 4Fe^(2+)(aq)+O_(2)(g) +4H_(2)O(l) rarr 2Fe_(2)O_(3)(s)+8H^(o+)`
`d.Fe_(2)O_(3)(aq)+xH_(2)O(l) rarr Fe_(2)O_(3).xH_(2)O`
Reason `(R) : ` Rusting is accelerated in the presence of `NaCl` and `CO_(2)`

Options

A. If both `(A)` and `(R)` are correct, and `(R)` is the correct explanation of `(A)`.
B. If both `(A)` and `(R)` are correct, but `(R)` is not the correct explanation of `(A)`.
C. If `(A)` is correct, but `(R)` is incorrect.
D. If `(A)` is incorrect, `(R)` is correct.

Answer

To solve the problem, we need to analyze the assertion (A) and the reason (R) provided in the question regarding the rusting of iron.

### Step-by-Step Solution:

1. **Understanding Assertion (A)**:
- The assertion states that rusting on the surface of iron involves several reactions:
- **Anodic Reaction**:
\[ \text{Fe(s)} \rightarrow \text{Fe}^{2+}(aq) + 2e^{-} \]
This indicates that iron is oxidized to ferrous ions (Fe²⁺) at the anodic site.
- **Cathodic Reaction**:
\[ \text{O}_{2}(g) + 4\text{H}^{+}(aq) + 4e^{-} \rightarrow 2\text{H}_{2}O(l) \]
This shows that oxygen is reduced to water at the cathodic site.
- **Overall Reaction**:
\[ 4\text{Fe}^{2+}(aq) + \text{O}_{2}(g) + 4\text{H}_{2}O(l) \rightarrow 2\text{Fe}_{2}O_{3}(s) + 8\text{H}^{+} \]
This represents the formation of rust (Fe₂O₃) from ferrous ions and oxygen.
- **Hydration of Rust**:
\[ \text{Fe}_{2}O_{3}(aq) + x\text{H}_{2}O(l) \rightarrow \text{Fe}_{2}O_{3} \cdot x\text{H}_{2}O \]
This indicates the formation of hydrated iron(III) oxide, commonly known as rust.

2. **Understanding Reason (R)**:
- The reason states that rusting is accelerated in the presence of NaCl and CO₂.
- NaCl (sodium chloride) can increase the conductivity of water, which can enhance the electrochemical reactions leading to rusting.
- CO₂ can dissolve in water to form carbonic acid (H₂CO₃), which can further corrode iron, thus accelerating rusting.

3. **Evaluating the Statements**:
- Both the assertion (A) and the reason (R) are correct.
- However, the reason (R) does not directly explain the specific reactions mentioned in assertion (A). Instead, it provides additional information about factors that can accelerate rusting.

4. **Conclusion**:
- Since both the assertion and reason are correct, but the reason is not the correct explanation of the assertion, the correct answer is:
- **Option B**: Both A and R are correct but R is not the correct explanation of A.