Statement-1: Photon has definite momentum though it has no rest mass.
Statement-2: Momentum of photon is due to its energy and therefore it has equivalent mass.

Options

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

Explanation

To solve the problem, we need to analyze both statements regarding photons and their properties.

### Step 1: Understanding Statement-1
**Statement-1:** "Photon has definite momentum though it has no rest mass."

- A photon is a quantum of light and is known to travel at the speed of light (c) in a vacuum.
- Although photons do not have rest mass (mass when at rest), they do carry momentum.
- The momentum (p) of a photon can be expressed using the equation:
\[ p = \frac{E}{c} \]
where \(E\) is the energy of the photon and \(c\) is the speed of light.

### Step 2: Understanding Statement-2
**Statement-2:** "Momentum of photon is due to its energy and therefore it has equivalent mass."

- The energy of a photon is given by:
\[ E = h \cdot f \]
where \(h\) is Planck's constant and \(f\) is the frequency of the photon.
- The concept of equivalent mass comes from Einstein's mass-energy equivalence principle, which states:
\[ E = mc^2 \]
Rearranging gives us the equivalent mass \(m\) of the photon as:
\[ m = \frac{E}{c^2} \]
- Substituting this into the momentum equation gives:
\[ p = mc = \frac{E}{c^2} \cdot c = \frac{E}{c} \]
- This shows that the momentum of the photon is indeed related to its energy, and while it does not have rest mass, it can be described in terms of equivalent mass.

### Conclusion
Both statements are correct:
- Statement-1 is true because photons have momentum despite having no rest mass.
- Statement-2 is also true because the momentum of a photon can be derived from its energy, and it can be described using the concept of equivalent mass.

### Final Answer
Both Statement-1 and Statement-2 are correct, and Statement-2 provides the correct explanation for Statement-1.

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