Which one of the following statements is correct-

Options

A. The oxidation number of oxygen in `KO_(2)` is zero
B. The specific conductance of an electrolyte solution decreases with increase in dilution
C. `Sn^(2+)` oxidises `Fe^(3+)`
D. `Zn//ZnSO_(4)` is a reference electrode

Explanation

To solve the question regarding which statement is correct, we will analyze each of the provided statements one by one.

### Step 1: Analyze the first statement
**Statement:** The oxidation number of oxygen in CO2 is zero.

**Analysis:**
The oxidation number of oxygen in carbon dioxide (CO2) is actually -2, not zero. In CO2, carbon has an oxidation state of +4, and each oxygen atom has an oxidation state of -2. Therefore, this statement is incorrect.

### Step 2: Analyze the second statement
**Statement:** Specific conductance of an electrolyte solution decreases with increase in dilution.

**Analysis:**
This statement is also incorrect. The specific conductance (or conductivity) of an electrolyte solution actually increases with dilution because dilution leads to the dissociation of more ions, which enhances conductivity. Therefore, this statement is false.

### Step 3: Analyze the third statement
**Statement:** Sn^2+ oxidizes Fe^3+.

**Analysis:**
This statement is incorrect as well. In electrochemical terms, Sn^2+ is a reducing agent and cannot oxidize Fe^3+. Instead, Fe^3+ can reduce Sn^2+. Thus, this statement is also false.

### Step 4: Analyze the fourth statement
**Statement:** Zn and Zn^2+ is the reference electrode.

**Analysis:**
This statement is correct. The zinc electrode (Zn/Zn^2+) can indeed be used as a reference electrode in electrochemical cells. It is often used in conjunction with the standard hydrogen electrode (SHE) to measure electrode potentials. Therefore, this statement is true.

### Conclusion
After analyzing all the statements, the correct answer is the fourth statement: **Zn and Zn^2+ is the reference electrode.**

---