Assertion `(A):` The mobility of `Na^(o+)` is lower than that of `K^(o+)` ion.
Reason `(R): ` The ionic mobility depends upon the effective radius of the ion.

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 question regarding the assertion and reason about the ionic mobility of Na⁺ and K⁺ ions, we can follow these steps:

### Step 1: Understand the Assertion
The assertion states that the mobility of Na⁺ (sodium ion) is lower than that of K⁺ (potassium ion).

### Step 2: Understand Ionic Mobility
Ionic mobility is defined as the ability of an ion to move through a medium, typically a solution, under the influence of an electric field. It is influenced by several factors, including the size of the ion.

### Step 3: Compare the Effective Radii
The effective radius of an ion is a measure of its size. In general, the ionic mobility is inversely proportional to the effective radius of the ion. This means that ions with a larger effective radius will have lower mobility.

### Step 4: Analyze the Sizes of Na⁺ and K⁺
- Sodium ion (Na⁺) has a smaller effective radius compared to potassium ion (K⁺).
- Therefore, K⁺ has a larger effective radius than Na⁺.

### Step 5: Conclude the Assertion
Since K⁺ has a larger effective radius, it will have higher mobility compared to Na⁺. Thus, the assertion that the mobility of Na⁺ is lower than that of K⁺ is **correct**.

### Step 6: Understand the Reason
The reason states that ionic mobility depends on the effective radius of the ion. This is also **correct** because, as mentioned, larger ions typically have lower mobility.

### Step 7: Conclusion
Both the assertion and the reason are correct, and the reason provides a correct explanation for the assertion. Therefore, the answer to the question is that both the assertion and reason are true, and the reason is the correct explanation of the assertion.

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

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