Assertion `(A): ` The emission of `alpha-` particles results in the formation of isodiapher of parent element.
Reason `(R) : ` Isodiaphers have same isotopic number.

Answer

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

### Step 1: Understand the Assertion
The assertion states: "The emission of alpha particles results in the formation of isodiaphers of the parent element."

**Explanation:**
- When an alpha particle (which consists of 2 protons and 2 neutrons) is emitted from a parent nucleus, the resulting daughter nucleus will have 2 fewer protons and 2 fewer neutrons than the parent nucleus.
- This means that the difference between the number of protons and neutrons (N - P) remains unchanged, leading to the formation of isodiaphers.

### Step 2: Understand the Reason
The reason states: "Isodiaphers have the same isotopic number."

**Explanation:**
- Isodiaphers are nuclides that have the same difference between the number of neutrons and protons (N - P), but different total numbers of protons and neutrons.
- The term "isotopic number" is often confused with "isotopes," but in this context, it refers to the difference between the number of neutrons and protons being the same.

### Step 3: Analyze the Relationship between Assertion and Reason
- The assertion is correct because the emission of alpha particles does indeed lead to the formation of isodiaphers, as explained.
- The reason is also correct because isodiaphers do have the same difference between the number of neutrons and protons (N - P).
- However, the reason does not directly explain the assertion. It simply states a fact about isodiaphers without linking it to the process of alpha emission.

### Conclusion
Both the assertion and reason are correct, but the reason is not the explanation for the assertion. Therefore, the correct answer to the question is that the assertion is true, the reason is true, but the reason does not explain the assertion.

### Final Answer
- Assertion (A) is true.
- Reason (R) is true, but it does not explain (A).