A : photon cannot transfer all of its energy to an isolated electron .
R : When energy of a photon is more then 1.02 MeV , It can materialize into two particles called electron and positron .

Options

A. If both Assertion & Reason are ture and the reason is the correct explanation of the assertion , then mark (1) .
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion , then mark (2) .
C. If Assertion is true statement but Reason is false , then mark (3)
D. If both Assertion and Reason are false statements , then mark (4) .

Answer

To solve the assertion and reason question, let's break down the concepts involved step by step.

### Step 1: Understanding the Assertion
The assertion states that a photon cannot transfer all of its energy to an isolated electron.

- **Explanation**: When a photon interacts with an isolated electron, it must conserve both energy and momentum. If a photon with energy \( E = h\nu \) (where \( h \) is Planck's constant and \( \nu \) is the frequency) were to transfer all its energy to the electron, the electron would need to gain momentum equal to that of the photon. However, since the electron has mass, it cannot simply take all the energy without also gaining momentum, which would violate conservation laws.

### Step 2: Understanding the Reason
The reason states that when the energy of a photon is greater than 1.02 MeV, it can materialize into two particles: an electron and a positron.

- **Explanation**: The energy threshold of 1.02 MeV corresponds to the combined rest mass energy of an electron and a positron (each has a rest mass energy of 0.511 MeV). If a photon has energy greater than this threshold, it can produce these two particles through a process known as pair production. This process conserves both energy and momentum, as the photon transforms its energy into the rest mass energy of the two particles.

### Step 3: Conclusion
- The assertion is **true** because a photon cannot transfer all its energy to an isolated electron due to conservation laws.
- The reason is also **true** because a photon with energy greater than 1.02 MeV can indeed materialize into an electron and a positron.

### Final Statement
The assertion is correct, and the reason is correct but does not correctly explain the assertion. Thus, the correct option is that both statements are true, but the reason is not the correct explanation for the assertion.