Assertion `(A) : ` The ratio of specific conductivity to the observed conductance does not depend upon the concentration of the solution taken in the conductivity cell.
Reason `(R) :` Specific conductivity decreases with dilution whereas observed conductance increases with the dilution.
(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, ( R ) is correct.

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, `(R)` is correct.

Explanation

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

### Step 1: Understanding Assertion (A)
The assertion states: "The ratio of specific conductivity to the observed conductance does not depend upon the concentration of the solution taken in the conductivity cell."

- **Specific Conductivity (κ)** is defined as the conductivity of a solution per unit length and area (κ = G * (l/a), where G is conductance, l is the length of the cell, and a is the area).
- **Observed Conductance (G)** is the actual conductance measured in the conductivity cell.
- The ratio of specific conductivity to observed conductance (κ/G) gives us the cell constant (l/a), which is a constant for a given cell design.

**Conclusion for Step 1**: The assertion is true because the cell constant does not depend on the concentration of the solution.

### Step 2: Understanding Reason (R)
The reason states: "Specific conductivity decreases with dilution whereas observed conductance increases with dilution."

- When a solution is diluted, the number of ions per unit volume decreases, leading to a decrease in specific conductivity (κ).
- However, as the solution is diluted, the total number of ions remains the same, which can lead to an increase in observed conductance (G) because the ions are more dispersed and can move more freely.

**Conclusion for Step 2**: The reason is also true, but it does not explain the assertion. The assertion is about the ratio being constant, while the reason discusses how specific conductivity and observed conductance change with dilution.

### Final Conclusion
Both the assertion (A) and reason (R) are correct, but (R) is not the correct explanation of (A). Therefore, the correct option is:

**(b) If both (A) and (R) are correct, but (R) is not the correct explanation of (A).**

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