Assertion (A): Transition metals have high melting point.
Reason (R): Transition metals have completely filled d-orbitals.

Options

A. Both A and Rare true and R is the correct explanation of A.
B. Both A and R are true but R is NOT the correct explanation of A.
C. A is true but R is false.
D. A is false and R is True

Explanation

To solve the question regarding the assertion and reason provided, we will analyze both statements step by step.

### Step 1: Analyze the Assertion (A)
**Assertion (A): Transition metals have high melting points.**

- Transition metals are known for their high melting points. This is primarily due to the strong metallic bonding present in these metals. The presence of partially filled d-orbitals allows for effective overlap between the d-orbitals of adjacent atoms, leading to stronger metallic bonds.

### Step 2: Analyze the Reason (R)
**Reason (R): Transition metals have completely filled d-orbitals.**

- This statement is incorrect. Transition metals actually have partially filled d-orbitals. The presence of unpaired electrons in these d-orbitals contributes to the strength of metallic bonding. If the d-orbitals were completely filled, the bonding characteristics would differ, and the melting points would not necessarily be high.

### Step 3: Conclusion
- The assertion is true because transition metals indeed have high melting points due to strong metallic bonding.
- The reason is false because transition metals do not have completely filled d-orbitals; they have partially filled d-orbitals.

### Final Answer
- The assertion (A) is true, while the reason (R) is false. Therefore, the correct conclusion is that the assertion is true, and the reason is false.