Given:
Buffer solution A: weak monoprotic acid and its sodium salt in the concentration ratio x : y, pH = (pH)1
Buffer solution B: same acid and its sodium salt in the concentration ratio y : x, pH = (pH)2
(pH)2 - (pH)1 = 1
(pH)1 - (pH)2 = 9.5

To solve this problem, we need to understand the concept of pH and the Henderson-Hasselbalch equation.

1. Introduction to pH:
pH is a measure of the acidity or alkalinity of a solution. It is defined as the negative logarithm of the hydrogen ion concentration ([H+]) in the solution.

2. Henderson-Hasselbalch equation:
The Henderson-Hasselbalch equation relates the pH of a buffer solution to the pKa (acid dissociation constant) of the weak acid and the ratio of the concentrations of the weak acid and its conjugate base.

pH = pKa + log([A-]/[HA])

where pH is the solution's pH, pKa is the acid dissociation constant, [A-] is the concentration of the conjugate base, and [HA] is the concentration of the weak acid.

3. Understanding the given information:
From the given information, we know that buffer solution A has a pH of (pH)1 and buffer solution B has a pH of (pH)2. We also know that the difference between (pH)2 and (pH)1 is 1 unit and the difference between (pH)1 and (pH)2 is 9.5 units.

4. Relating pH to pKa:
Since the solutions are buffer solutions of the same weak acid and its sodium salt, the pKa value will be the same for both solutions.

From the Henderson-Hasselbalch equation, we can see that the pH of a buffer solution is directly related to the pKa value. As the pKa value increases, the pH of the solution also increases.

5. Analyzing the given options:
a) pKa = 4.75
If this option is correct, it means that the pKa value is the same for both buffer solutions. However, this option does not provide any information about the concentration ratio.

b) x/y = 2.36
If this option is correct, it means that the concentration ratio of buffer solution A is 2.36. However, it does not provide any information about the pH values.

c) x/y = 3.162
If this option is correct, it means that the concentration ratio of buffer solution A is 3.162. However, it does not provide any information about the pH values.

d) pKa = 5.25
If this option is correct, it means that the pKa value is the same for both buffer solutions. However, this option does not provide any information about the concentration ratio.

6. Conclusion:
Based on the given information and the understanding of pH and the Henderson-Hasselbalch equation, the correct options are a) pKa = 4.75 and c) x/y = 3.162. These options satisfy the given conditions and provide a consistent explanation for the pH values of the buffer solutions.