Assertion `(A): beta-` particles have greater penetrating power than `alpha-` rays but less than `gamma-`rays.
Reason `(R) : beta-` particles are lighter than `alpha-`particles but heavier than `gamma.`

Options

A. If both `(A)` and `(R)` are correct , and `(R)` is the correct explanation of `(A)`
B. If both `(A)` and `(R)` are correct, but (R) is not the correct explanation of `(A)`
C. If `(A)` is correct, but `(R)` is incorrect.
D. If `(A)` is incorrect, but `(R)` is correct.

Explanation

To solve the question, we need to analyze both the assertion and the reason provided.

### Step 1: Understanding the Assertion
The assertion states that beta- particles have greater penetrating power than alpha rays but less than gamma rays.

**Explanation**:
- Alpha particles (α) are relatively heavy and positively charged (composed of 2 protons and 2 neutrons). Due to their mass and charge, they interact more strongly with matter, which limits their penetrating ability. They can be stopped by a sheet of paper or even the outer layer of human skin.
- Beta particles (β) are much lighter and negatively charged (essentially electrons). They have a greater penetrating ability than alpha particles because they are less likely to interact with matter due to their smaller mass.
- Gamma rays (γ) are electromagnetic radiation and have no mass or charge. They have the highest penetrating power of all three types of radiation, being able to pass through most materials, including human tissue and lead, to some extent.

### Step 2: Understanding the Reason
The reason states that beta particles are lighter than alpha particles but heavier than gamma particles.

**Explanation**:
- Beta particles are indeed lighter than alpha particles, which aligns with the assertion.
- Gamma rays have no mass, so they are considered lighter than both alpha and beta particles. Therefore, the statement that beta particles are heavier than gamma is correct in the context of mass, as gamma rays have zero mass.

### Step 3: Conclusion
Both the assertion and the reason are correct. The reason provided correctly explains why beta particles have greater penetrating power than alpha particles but less than gamma rays.

### Final Answer
Both assertion (A) and reason (R) are correct, and the reason (R) is the correct explanation of the assertion (A).