Assertion:Kohlrausch law helps to find the molar conductivity of weak electrolyte at infinite dilution.
Reason:Molar conductivity of a weak electrolyte at infinite dilution cannot be determined experimentally.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion .
B. If both assertion and reason are true but reason is not the correct explanation of assertion .
C. If assertion is true but reason is false .
D. If both assertion and reason are false .

Answer

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

### Step 1: Understand the Assertion
The assertion states that "Kohlrausch's law helps to find the molar conductivity of weak electrolyte at infinite dilution."

- **Kohlrausch's Law**: This law states that the molar conductivity of an electrolyte at infinite dilution (denoted as λm0) is equal to the sum of the molar conductivities of its constituent ions at infinite dilution.
- For weak electrolytes, which do not dissociate completely in solution, Kohlrausch's law is particularly useful because it allows us to calculate their molar conductivity using the known values of strong electrolytes.

### Step 2: Understand the Reason
The reason states that "molar conductivity of a weak electrolyte at infinite dilution cannot be determined experimentally."

- This statement is true in the sense that weak electrolytes do not fully dissociate in solution, making it difficult to measure their conductivity directly. However, we can still use Kohlrausch's law to calculate their molar conductivity indirectly using the molar conductivities of strong electrolytes.

### Step 3: Analyze the Relationship
Now we need to determine if the assertion and reason are true or false:

- **Assertion**: True. Kohlrausch's law is indeed used to find the molar conductivity of weak electrolytes at infinite dilution.
- **Reason**: False. While it is challenging to determine the molar conductivity of weak electrolytes experimentally, it can still be calculated using Kohlrausch's law.

### Step 4: Conclusion
Given the analysis:
- The assertion is true.
- The reason is false.

Thus, the correct answer to the question is that the assertion is true and the reason is false.

### Final Answer
The correct option is **3**: Assertion is true, Reason is false.

---