(A): If a conducting medium is placed between two charges, then electric force between them becomes zero.
(R ): Reduction in a force due to introduced material is inversely proportional to its dielectric constant.

Options

A. Both .A. and .R. are true and .R. is the correct explanation of .A.
B. Both .A. and .R. are tru and .R. is not the correct explanation of .A.
C. A. is true and .R. is false
D. A. is false and .R. is true

Answer

To analyze the given statements (A) and (R), we will break down the concepts involved and provide a step-by-step solution.

### Step-by-Step Solution:

1. **Understanding Statement (A)**:
- The statement claims that if a conducting medium is placed between two charges, the electric force between them becomes zero.
- In electrostatics, when a conductor is placed in an electric field, it polarizes and redistributes its charges. This redistribution creates an opposing electric field that cancels the original field between the two charges.

2. **Effect of a Conductor**:
- When a conducting medium is placed between two point charges \( q_1 \) and \( q_2 \), the charges on the conductor will rearrange such that the electric field inside the conductor is zero.
- As a result, the net electric field between the two charges becomes zero, leading to zero force between them.

3. **Understanding Statement (R)**:
- The reasoning states that the reduction in force due to the introduced material is inversely proportional to its dielectric constant.
- The dielectric constant \( k \) is a measure of how much a material can reduce the electric field compared to a vacuum.

4. **Force in a Dielectric Medium**:
- The electrostatic force \( F \) between two charges in a vacuum is given by:
\[ F = \frac{1}{4 \pi \epsilon_0} \frac{q_1 q_2}{r^2} \]
- When a dielectric medium is introduced, the force becomes:
\[ F' = \frac{1}{4 \pi \epsilon_0 k} \frac{q_1 q_2}{r^2} \]
- As the dielectric constant \( k \) increases, the force \( F' \) decreases, indicating that the force is inversely proportional to \( k \).

5. **Conclusion**:
- Since the conducting medium effectively cancels the electric field between the charges, the force becomes zero.
- The reasoning that the reduction in force is inversely proportional to the dielectric constant is also correct because, for a conductor, \( k \) approaches infinity, leading to a force of zero.
- Therefore, both statements (A) and (R) are true, and (R) is the correct explanation of (A).

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