Assertion: The de-broglie wavelength equation has significance for any microscopic or submicroscopic particles.
Reason : The de-broglie wavelength is inversely proportional to the mass of the object if velocity is constant.

Answer

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

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that the de Broglie wavelength equation has significance for any microscopic or submicroscopic particles.
- The de Broglie wavelength (\( \lambda \)) is given by the formula:
\[ \lambda = \frac{h}{p} \]
where \( h \) is Planck's constant and \( p \) is the momentum of the particle.

2. **Understanding the Reason**:
- The reason states that the de Broglie wavelength is inversely proportional to the mass of the object if the velocity is constant.
- Since momentum \( p \) is defined as \( p = mv \) (where \( m \) is mass and \( v \) is velocity), we can rewrite the de Broglie wavelength as:
\[ \lambda = \frac{h}{mv} \]
- If the velocity \( v \) is constant, then the de Broglie wavelength \( \lambda \) becomes inversely proportional to the mass \( m \):
\[ \lambda \propto \frac{1}{m} \]

3. **Analyzing the Significance**:
- For microscopic and submicroscopic particles (like electrons, protons, etc.), the mass is small, which means that the de Broglie wavelength can be significant and measurable.
- In contrast, for macroscopic particles (like a baseball or a car), the mass is large, leading to a very small de Broglie wavelength, which is negligible and not significant in practical terms.

4. **Conclusion**:
- Both the assertion and the reason are true:
- The assertion is true because the de Broglie wavelength is indeed significant for microscopic and submicroscopic particles.
- The reason is also true as it correctly explains that the de Broglie wavelength is inversely proportional to mass when velocity is constant.

5. **Final Statement**:
- Therefore, both the assertion and reason are true, and the reason is a correct explanation of the assertion.

### Final Answer:
- **Assertion**: True
- **Reason**: True
- **Explanation**: The reason correctly explains the assertion.