Radioactivity is affected by:

Options

A. temperature
B. pressure
C. electric and magnetic field
D. none of these

Answer

**Step-by-Step Solution:**

1. **Understanding Radioactivity**:
- Radioactivity is defined as the spontaneous emission of radiation in the form of particles or high-energy photons due to nuclear reactions.

2. **Key Characteristics of Radioactivity**:
- The decay of radioactive substances occurs at a rate that is proportional to the number of undecayed nuclei present. This means that the more undecayed nuclei there are, the more radiation will be emitted.

3. **Mathematical Representation**:
- The rate of radioactive decay can be expressed mathematically as:
\[ \frac{dn}{dt} = -\lambda n \]
- Here, \( \frac{dn}{dt} \) is the rate of decay, \( n \) is the number of undecayed atoms at time \( t \), and \( \lambda \) is the decay constant.

4. **Analyzing the Factors**:
- The question asks whether radioactivity is affected by temperature, pressure, electric fields, or magnetic fields.
- From the equation, it is clear that the rate of decay depends solely on the number of undecayed atoms (n) and the decay constant (λ).

5. **Conclusion**:
- Since the rate of radioactive decay does not change with temperature, pressure, electric fields, or magnetic fields, we conclude that radioactivity is not affected by any of these factors.

6. **Final Answer**:
- Therefore, the correct answer is **none of these**.

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