Assertion : Radioactive heavy nuclei decay by a series of `alpha- and //or beta-`emission, to form a stable isotope of lead
Reaosn : Radioactivity is a physical phenomenon

Options

A. If both assertion and reason are true and the reason is the correct explanation of the assertion
B. If both assertion and reason are true but reason is not the correct explanantion of the assertion
C. If assertion is true but reason is false
D. If the assertion and reason both are false

Explanation

To solve the question, we need to analyze both the assertion and the reason given in the statement.

### Step 1: Analyze the Assertion
The assertion states: "Radioactive heavy nuclei decay by a series of alpha and/or beta emissions to form a stable isotope of lead."

- **Understanding the Assertion**:
- Heavy nuclei, such as those of uranium or thorium, undergo radioactive decay.
- This decay can involve the emission of alpha particles (helium nuclei) and beta particles (electrons or positrons).
- The assertion claims that this process leads to the formation of a stable isotope of lead.

- **Evaluation**:
- While it is true that heavy nuclei decay through alpha and beta emissions, the final stable isotope is not always lead. It can be other stable isotopes as well, depending on the decay chain.
- Therefore, the assertion is partially correct but misleading because it implies that lead is the only stable product.

### Step 2: Analyze the Reason
The reason states: "Radioactivity is a physical phenomenon."

- **Understanding the Reason**:
- The term "physical phenomenon" typically refers to observable changes that do not involve changes in the identity of the substance, such as phase changes (solid to liquid).

- **Evaluation**:
- Radioactivity involves nuclear reactions and changes in the identity of the element (e.g., uranium decaying into lead). This is a nuclear phenomenon rather than a purely physical one.
- Thus, the reason is incorrect.

### Conclusion
- **Final Evaluation**:
- Both the assertion and the reason are incorrect. The assertion is misleading as it suggests that lead is the only stable product, and the reason mischaracterizes radioactivity as a physical phenomenon.

### Answer: Both assertion and reason are false.

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