(A) : Crystalline solids have sharp and characteric melting points.
(R) : Crystalline solids have definite heat of fusion.

Options

A. Both (A) and (R) are true. (R) properly explain (A)
B. Both (A) and (R) are true. (R) does not explain (A)
C. (A) is true. (R) is false
D. (A) is false. (R) is true

Answer

To solve the question, we need to analyze both the assertion and the reason provided:

**Assertion (A)**: Crystalline solids have sharp and characteristic melting points.
**Reason (R)**: Crystalline solids have definite heat of fusion.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- Crystalline solids are known for their orderly and repeating arrangement of particles (atoms, ions, or molecules).
- This orderly arrangement leads to a specific structure, which results in a sharp and characteristic melting point.
- When a crystalline solid is heated, it will melt at a specific temperature, which is a defining property of that solid.

**Hint**: Recall that the orderly arrangement of particles in a crystalline solid contributes to its unique properties.

2. **Understanding the Reason**:
- The reason states that crystalline solids have a definite heat of fusion.
- Heat of fusion is the amount of energy required to change a substance from solid to liquid at its melting point.
- This is true for crystalline solids, as they require a specific amount of energy to overcome the forces holding the particles in their fixed positions.

**Hint**: Consider how the energy required for melting relates to the properties of solids.

3. **Evaluating the Relationship**:
- Both the assertion and the reason are true statements.
- However, the reason does not adequately explain why crystalline solids have sharp melting points.
- The sharp melting point is a result of the ordered structure, while the definite heat of fusion is a property that describes the energy change during melting.

**Hint**: Think about whether the reason logically supports the assertion.

4. **Conclusion**:
- Since both statements are true but the reason does not explain the assertion, the correct conclusion is:
- Both A and R are true, but R is not the correct explanation for A.

### Final Answer:
Both A and R are true, but R is not the correct explanation for A.

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