Assertion : Mass of moving photon varies inversely as the wavelength .
Reason : Energy of the particle `= Mass xx (Speed of light)^(2)`

Options

A. If both the Asseration and Reason are true and reason explains the Assertion :
B. If both the Assertion and Reason are true but reason does ot explain the Assertion :
C. If Assertion is true but reason false
D. If Assertion is false but reason is true

Answer

To solve the 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 mass of a moving photon varies inversely as the wavelength. We need to verify this statement.

2. **Using de Broglie Wavelength Formula**:
- According to de Broglie's hypothesis, the wavelength (λ) of a particle is given by:
\[ \lambda = \frac{h}{mv} \]
where \(h\) is Planck's constant, \(m\) is the mass of the particle, and \(v\) is its velocity.

3. **Applying to a Photon**:
- For a photon, it travels at the speed of light (c). Thus, we can substitute \(v\) with \(c\):
\[ \lambda = \frac{h}{mc} \]

4. **Rearranging the Formula**:
- Rearranging the equation to express mass in terms of wavelength:
\[ mc = \frac{h}{\lambda} \]
\[ m = \frac{h}{\lambda c} \]

5. **Analyzing the Relationship**:
- From the equation \(m = \frac{h}{\lambda c}\), we can see that mass (m) is inversely proportional to the wavelength (λ). This confirms that the assertion is true.

6. **Understanding the Reason**:
- The reason states that the energy of a particle is given by \(E = mc^2\). This is Einstein's mass-energy equivalence principle.

7. **Evaluating the Reason**:
- While the reason is true, it does not directly explain the assertion about the relationship between mass and wavelength for a photon. The assertion is derived from the de Broglie wavelength formula, not from the mass-energy equivalence.

8. **Conclusion**:
- Both the assertion and the reason are true, but the reason does not explain the assertion. Thus, the correct answer is that both the assertion and reason are true, but the reason is not the correct explanation for the assertion.

### Final Answer:
Both the assertion and reason are true, but the reason does not explain the assertion.