All transition elements are d-block elements, but all d-block elements are not transition elements. Which the following is true.

Explanation

To solve the question, we need to understand the definitions and characteristics of d-block elements and transition elements.

### Step-by-Step Solution:

1. **Definition of d-block Elements**:
- d-block elements are those elements in which the last electron enters the d-subshell. This includes groups 3 to 12 of the periodic table.

2. **Definition of Transition Elements**:
- Transition elements are a subset of d-block elements that have partially filled d-orbitals in their elemental or common oxidation states. This means that they exhibit certain properties such as variable oxidation states, formation of colored compounds, and the ability to form complex ions.

3. **Examples of d-block Elements**:
- Manganese (Mn): The electronic configuration is [Ar] 3d^5 4s^2. Here, the last electron enters the d-subshell, making it a transition element.
- Zinc (Zn): The electronic configuration is [Ar] 3d^10 4s^2. The last electron enters the 4s subshell, and thus, while it is a d-block element, it does not qualify as a transition element because the d-orbital is fully filled.

4. **Conclusion**:
- Therefore, the statement "All transition elements are d-block elements" is true because transition elements are defined as those d-block elements with partially filled d-orbitals.
- The statement "All d-block elements are not transition elements" is also true because elements like zinc, cadmium, and mercury have fully filled d-orbitals and do not exhibit the typical properties of transition metals.

### Final Answer:
Both statements are true.

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