The decay of radioactive substance can neither be accelerated nor slowed by any physical or chemical method..

Answer

**Solution:**

To determine whether the statement "The decay of radioactive substance can neither be accelerated nor slowed by any physical or chemical method" is true or false, we need to analyze the nature of radioactive decay.

1. **Understanding Radioactive Decay**:
- Radioactive decay is a spontaneous process where unstable atomic nuclei lose energy by emitting radiation. This process results in the transformation of the original nucleus into a different element or a different isotope of the same element.

2. **Nature of the Decay Process**:
- The decay of a radioactive substance is governed by the laws of quantum mechanics and is inherently random. The time it takes for half of a sample of a radioactive substance to decay is characterized by its half-life, which is a constant for each radioactive isotope.

3. **Energy Requirements**:
- The decay process involves overcoming the strong nuclear forces that hold the protons and neutrons together in the nucleus. This process requires a significant amount of energy, which cannot be supplied through ordinary physical or chemical means.

4. **Influence of External Conditions**:
- While external conditions (like temperature and pressure) can affect chemical reactions, they do not influence the rate of radioactive decay. The decay rate is a fundamental property of the isotope and is not affected by external environmental factors.

5. **Conclusion**:
- Since the decay process is spontaneous and cannot be influenced by physical or chemical methods, the statement is indeed **true**.

**Final Answer**: The statement is **True**.

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