Which of the following reactions is an example of nucleophilic substitution reaction?

Options

A. `RX+Mg to RMgX`
B. `RX +KOH to ROH +KX `
C. `2RK +2Na to R-R +2NaX `
D. `RX +H_(2) to RH +HX `

Explanation

To determine which of the following reactions is an example of a nucleophilic substitution reaction, we need to understand the definition and mechanism of nucleophilic substitution reactions.

### Step-by-Step Solution:

1. **Understanding Nucleophilic Substitution**:
- A nucleophilic substitution reaction involves the replacement of a leaving group (often a halide) by a nucleophile. The nucleophile is typically an electron-rich species that donates a pair of electrons to form a new bond.

2. **Identifying the Components**:
- In a nucleophilic substitution reaction, we generally have a substrate (often an alkyl halide, denoted as RX), a nucleophile (like OH⁻ or NH₃), and a leaving group (like X⁻).

3. **Analyzing the Given Reactions**:
- We need to analyze each reaction option provided to identify if it fits the criteria of a nucleophilic substitution reaction.

4. **Example Reaction**:
- Consider the reaction:
\[ R-X + KOH \rightarrow R-OH + KX \]
- Here, KOH dissociates into K⁺ and OH⁻. The OH⁻ acts as a nucleophile and replaces the X in RX, forming R-OH and KX. This is a classic example of a nucleophilic substitution reaction.

5. **Conclusion**:
- After analyzing the reactions, the correct example of a nucleophilic substitution reaction is the one where a nucleophile (like OH⁻) replaces a leaving group (like X⁻) in the substrate (RX).

### Final Answer:
The reaction that is an example of a nucleophilic substitution reaction is:
\[ R-X + KOH \rightarrow R-OH + KX \]