Read the passage given below and answer the question:
The d block elements are the 40 elements contained in the four rows of ten columns (3-12) in the periodic table. As all the d block elements are metallic, the term d-block metals is synonymous. This set of d-block elements is also often identified as the transition metals, but sometimes the group 12 elements (zinc, cadmium, mercury) are excluded from the transition metals as the transition elements are defined as those with partly filled d or f shells in their compounds. Inclusion of the elements zinc, cadmium and mercury is necessary as some properties of the group 12 elements are appropriate logically to include with a discussion of transition metal chemistry.
The term transition element or transition metal appeared to derive from early studies of periodicity such as the Mendeleev periodic table of the elements. His horizontal table of the elements was an attempt to group the elements together so that the chemistry of elements might be explained and predicted. In this table there are eight groups labeled I-VIII with each subdivided into A and B subgroups. Mendeleev recognized that certain properties of elements in Group VIII are related to those of some of the elements in Group VII and those at the start of the next row Group I. In that sense, these elements might be described as possessing properties transitional from one row of the table to the next. (source: Winter, M. J. (2015). D- block Chemistry (Vol. 27). Oxford University Press, USA.)
In the following question, a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the choices on the basis of the above passage.
Assertion: Group 12 elements are not considered as transition metals.
Reason: Transition metals are those which have incompletely filled d shell in their compounds.

Options

A. Assertion and reason both are correct statements and reason is correct explanation for assertion.
B. Assertion and reason both are correct statements but reason is not correct explanation for assertion.
C. Assertion is correct statement but reason is wrong statement.
D. Assertion is wrong statement but reason is correct statement.

Answer

To solve the question, we need to analyze the assertion and reason statements based on the information provided in the passage.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states: "Group 12 elements are not considered as transition metals."
- According to the passage, the group 12 elements (zinc, cadmium, and mercury) are often excluded from the transition metals because they have completely filled d-orbitals (3d10 for zinc, 4d10 for cadmium, and 5d10 for mercury). Therefore, this assertion is **true**.

2. **Understanding the Reason**:
- The reason states: "Transition metals are those which have incompletely filled d shell in their compounds."
- The passage confirms that transition metals are defined as those with partly filled d or f shells. Since the group 12 elements have completely filled d-orbitals, this statement is also **true**.

3. **Evaluating the Relationship**:
- The assertion is true, and the reason is true as well. Furthermore, the reason correctly explains why the assertion is true, as it clarifies the definition of transition metals.

4. **Conclusion**:
- Since both the assertion and reason are true, and the reason provides a correct explanation for the assertion, the correct answer is that both statements are true and the reason is the correct explanation of the assertion.

### Final Answer:
Both the assertion and reason are true, and the reason is the correct explanation of the assertion.

---