Assertion : Sodium chloride (NaCl) is a stable ionic solid.
Reason : NaCl has high lattice enthalpy.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion.
B. If both assertion and reason are true but reason in not the correct explanation of assertion.
C. If assertion is true but reason is false.
D. If both assertion and reason are false.

Answer

To solve the assertion and reason question regarding sodium chloride (NaCl), we will analyze both the assertion and the reason step by step.

### Step 1: Analyze the Assertion
**Assertion:** Sodium chloride (NaCl) is a stable ionic solid.

- Sodium chloride is formed from sodium (Na) and chlorine (Cl). Sodium has one electron in its outer shell (2, 8, 1) and chlorine has seven electrons in its outer shell (2, 8, 7).
- Sodium loses one electron to achieve a stable electronic configuration (octet), forming a Na⁺ ion.
- Chlorine gains that electron to complete its octet, forming a Cl⁻ ion.
- The electrostatic attraction between the positively charged Na⁺ ions and negatively charged Cl⁻ ions results in the formation of a stable ionic bond.

**Conclusion:** The assertion is true because NaCl is indeed a stable ionic solid.

### Step 2: Analyze the Reason
**Reason:** NaCl has high lattice enthalpy.

- Lattice enthalpy (or lattice energy) refers to the amount of energy released when gaseous ions combine to form an ionic solid or the energy required to separate the solid into its gaseous ions.
- In the case of NaCl, the lattice energy is high due to the strong electrostatic forces of attraction between the Na⁺ and Cl⁻ ions.
- The greater the charge of the ions and the smaller their size, the higher the lattice energy. Na⁺ and Cl⁻ are both relatively small ions with a strong charge interaction, leading to a high lattice enthalpy.

**Conclusion:** The reason is also true because NaCl does have a high lattice enthalpy, which contributes to its stability.

### Step 3: Determine the Relationship
- Both the assertion and the reason are true.
- The reason (high lattice enthalpy) correctly explains why sodium chloride is a stable ionic solid.

### Final Conclusion
Both the assertion and the reason are true, and the reason is the correct explanation of the assertion. Therefore, the correct answer is option A.

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