Which of the following statements is//are correct ?

Options

A. Protic solvents solvate the nucleophile, lower enthalpy of nucleophiles, increase `Delta G`, and decrease the reaction rate of `SN^2` reaction.
B. `SN^1` reactions are favoured in protic solvents.
C. Crown ether increases the reactivity of nucleophile by solvating its cation.
D. `SN^2` reactions are more favoured in protic solvents.

Explanation

To determine which statements are correct regarding SN1 and SN2 reactions in the context of protic solvents and crown ethers, let's analyze each statement step by step.

### Step-by-Step Solution:

1. **Understanding Protic Solvents**:
- Protic solvents are those that have hydrogen atoms attached to electronegative atoms like oxygen or nitrogen. They can donate protons (H⁺) to solutes.
- This property allows protic solvents to solvate nucleophiles effectively.

**Hint**: Recall that protic solvents can stabilize nucleophiles by solvation, which can affect reaction rates.

2. **Evaluating Statement A**:
- Statement A claims that protic solvents solvate nucleophiles, which lowers the enthalpy of nucleophiles, increases ΔG, and decreases the reaction rate of SN2 reactions.
- This statement is correct because the solvation of nucleophiles by protic solvents can indeed lower their reactivity, leading to a higher activation energy (ΔG) and thus a slower reaction rate for SN2 reactions.

**Hint**: Consider how solvation affects nucleophile reactivity in SN2 mechanisms.

3. **Evaluating Statement B**:
- Statement B states that SN1 reactions are favored in protic solvents.
- This is also correct because protic solvents stabilize the carbocation intermediate formed during the ionization of the substrate, which is essential for SN1 reactions.

**Hint**: Think about the role of solvent in stabilizing charged intermediates in SN1 reactions.

4. **Evaluating Statement C**:
- Statement C asserts that crown ethers increase the reactivity of nucleophiles while solvating their cations.
- This statement is true as crown ethers can complex with cations (like K⁺) and effectively solvate them, which enhances the nucleophilicity of the anion.

**Hint**: Remember that crown ethers can selectively bind cations, affecting the overall reactivity of nucleophiles.

5. **Evaluating Statement D**:
- Statement D claims that SN2 reactions are more favored in protic solvents.
- This statement is incorrect. SN2 reactions are generally favored in aprotic solvents because protic solvents can hinder the nucleophile's approach to the electrophile due to solvation.

**Hint**: Recall the differences in solvent effects on SN1 and SN2 mechanisms.

### Conclusion:
The correct statements are A, B, and C. Statement D is incorrect.

### Final Answer:
- **Correct Statements**: A, B, C
- **Incorrect Statement**: D