Assertion A beam of charged particles is employed in the treatment of cancer.
Reason Charged particles on passing through a material medium loss their energy by causing ionisation of the atoms along their path.

Options

A. If both Assertion and Reason are true and Reason is the correct explanation of Assetion.
B. If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
C. If Assetion is true but Reason is false.
D. If both Assertion and Reason are false.

Explanation

To analyze the given statement, we will break it down into the assertion and the reason, and evaluate their validity step by step.

### Step 1: Understanding the Assertion
The assertion states that "A beam of charged particles is employed in the treatment of cancer."

- **Explanation**: In cancer treatment, particularly in radiation therapy, beams of charged particles such as protons or heavy ions are indeed used. These particles can effectively target and destroy cancerous cells.

### Step 2: Understanding the Reason
The reason states that "Charged particles on passing through a material medium lose their energy by causing ionization of the atoms along their path."

- **Explanation**: When charged particles travel through a material medium (like human tissue), they interact with the atoms in that medium. This interaction often results in the ionization of those atoms, meaning that electrons are knocked off the atoms, leading to energy loss for the charged particles.

### Step 3: Evaluating the Truth of Assertion and Reason
- **Assertion**: True. Charged particle beams are indeed used in cancer treatment.
- **Reason**: True. Charged particles lose energy through ionization as they pass through materials.

### Step 4: Analyzing the Relationship Between Assertion and Reason
While both the assertion and the reason are true, we need to determine if the reason provides a correct explanation for the assertion.

- The assertion explains the application of charged particles in cancer treatment, while the reason describes the mechanism of energy loss due to ionization. Although both statements are true, the reason does not directly explain why charged particles are used in cancer treatment.

### Conclusion
Both the assertion and the reason are true, but the reason does not provide a correct explanation for the assertion. Therefore, the correct answer is that both are true, but the reason is not the correct explanation of the assertion.

### Final Answer
The correct option is: Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion.

---