Assertion: Mercuryis not considered as a transition element.
Reason: Mercury is liquid.

Options

A. If both (A) and (R) are correct and (R) is the correct explanation of (A).
B. If both (A) and (R) are correct, but (R) is not the correct explanation of (A).
C. If (A) is correct, but (R) is incorrect.
D. If (A) is incorrect but (R) is correct.

Explanation

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

### Step 1: Understand the Assertion
The assertion states that "Mercury is not considered a transition element."
- Transition elements are defined as d-block elements that have unpaired electrons in their d-orbitals.

### Step 2: Analyze Mercury's Electron Configuration
Mercury (Hg) has the electronic configuration of:
\[ \text{[Xe]} 4f^{14} 5d^{10} 6s^2 \]
- Here, the d-orbital is completely filled (10 electrons), meaning there are no unpaired electrons.

### Step 3: Understand the Reason
The reason states that "Mercury is liquid."
- While it is true that mercury is the only metal that is liquid at room temperature, this property does not determine whether it is a transition element or not.

### Step 4: Conclusion
- Since mercury has a filled d-orbital (d10 configuration) and no unpaired electrons, it does not qualify as a transition element.
- Therefore, the assertion is correct, but the reason provided does not correctly explain why mercury is not a transition element.

### Final Answer
- Assertion: True (Mercury is not considered a transition element).
- Reason: True (Mercury is liquid), but it is not the correct explanation for the assertion.