Assertion: Between `alpha, beta and gamma` radiations, penetrating power of `gamma`-rays is maximum.
Reason : Ionising power of `gamma`-rays is least.

Options

A. (a) If both Assertion and Reason are true and Reason is correct explanation of the Assertion.
B. (b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
C. (c) If Assertion is true, but the Reason is false.
D. (d) If Assertion is false but the Reason is true.

Explanation

To solve the assertion and reason question, let's break down the concepts of penetrating power and ionizing power of alpha, beta, and gamma radiations step by step.

### Step 1: Understand the Assertion
The assertion states that "between alpha, beta, and gamma radiations, the penetrating power of gamma rays is maximum."

- **Penetrating Power**: This refers to the ability of radiation to pass through materials. The higher the penetrating power, the deeper the radiation can penetrate into a substance.

### Step 2: Understand the Reason
The reason provided is that "the ionizing power of gamma rays is least."

- **Ionizing Power**: This refers to the ability of radiation to ionize atoms, which means it can remove electrons from atoms, creating ions. Higher ionizing power means more interaction with matter, which typically results in less penetrating power.

### Step 3: Compare the Penetrating and Ionizing Powers of Alpha, Beta, and Gamma
1. **Alpha Radiation**:
- **Penetrating Power**: Very low (can penetrate only about 0.01 mm of lead).
- **Ionizing Power**: Very high (can ionize many atoms due to its charge and mass).

2. **Beta Radiation**:
- **Penetrating Power**: Moderate (can penetrate about 0.1 mm of lead).
- **Ionizing Power**: Moderate (less than alpha but more than gamma).

3. **Gamma Radiation**:
- **Penetrating Power**: Very high (can penetrate up to 10 cm of lead).
- **Ionizing Power**: Very low (least among the three types of radiation).

### Step 4: Establish the Relationship
From the comparison:
- Alpha has the least penetrating power but the highest ionizing power.
- Beta has moderate values for both penetrating and ionizing powers.
- Gamma has the highest penetrating power but the least ionizing power.

### Step 5: Conclusion
- The assertion is true: Gamma rays indeed have the maximum penetrating power.
- The reason is also true: Gamma rays have the least ionizing power.

Since the reason correctly explains the assertion, we conclude that both the assertion and reason are true, and the reason is the correct explanation of the assertion.

### Final Answer
Both assertion and reason are true, and the reason is the correct explanation for the assertion.