Assertion (A): `pK_(a)` of a weak acid become equal of the `pH` of the solution at the mid-point of titration.
Reason (R) : The molar concentration of the proton donor an proton acceptor beomes equal at the mid-point.

Options

A. Statement-1 is True, Statement-2 is True, Statement-2 is a correct explanation for Statement-1
B. Statement-1 is True, Statement-2 is True, Statement-2 is NOT a correct explanation for Statement-1
C. Statement-1 is True, Statement-2 is False
D. Statement-1 is False, Statement-2 is True

Answer

To solve the question, we need to analyze the assertion (A) and reason (R) provided:

**Assertion (A):** The \( pK_a \) of a weak acid becomes equal to the \( pH \) of the solution at the midpoint of titration.

**Reason (R):** The molar concentration of the proton donor and proton acceptor becomes equal at the midpoint.

### Step-by-Step Solution:

1. **Understanding the Midpoint of Titration:**
- In a titration of a weak acid (HA) with a strong base (like NaOH), the midpoint of the titration is the point at which half of the weak acid has been neutralized. At this point, half of the acid (HA) has been converted to its conjugate base (A⁻).

2. **Concentration of Acid and Conjugate Base:**
- At the midpoint, if we start with 1 mole of HA, then 0.5 moles of HA remain, and 0.5 moles of A⁻ are formed. Therefore, the concentrations of HA and A⁻ are equal.

3. **Using the Henderson-Hasselbalch Equation:**
- The Henderson-Hasselbalch equation is given by:
\[ pH = pK_a + \log\left(\frac{[A^-]}{[HA]}\right) \]
- Since at the midpoint, \([A^-] = [HA]\), the ratio \(\frac{[A^-]}{[HA]} = 1\). Thus, \(\log(1) = 0\).

4. **Conclusion from the Equation:**
- Substituting this into the Henderson-Hasselbalch equation gives:
\[ pH = pK_a + 0 \implies pH = pK_a \]
- Therefore, the assertion that \( pK_a \) of the weak acid becomes equal to the \( pH \) of the solution at the midpoint of titration is true.

5. **Analyzing the Reason:**
- The reason states that the molar concentration of the proton donor (HA) and the proton acceptor (A⁻) becomes equal at the midpoint. This is also true, as we have established that at the midpoint, the concentrations of HA and A⁻ are indeed equal.

6. **Determining the Relationship:**
- While both statements are true, the reason does not fully explain why \( pK_a \) equals \( pH \) at the midpoint. The equality of concentrations leads to the equality of \( pK_a \) and \( pH \), but the reason does not articulate this relationship clearly.

### Final Answer:
- The assertion is true, and the reason is true, but the reason is not a correct explanation for the assertion. Therefore, the correct option is **B**: Statement 1 is true, Statement 2 is true, but Statement 2 is not a correct explanation for Statement 1.