The phenomenon of interaction of anions and cations furnished by a electrolyte with the `H^(+)` and `OH^(-)` ions of water to produce acidity or alkalinity is known as hydrolysis. In hydrolysis :

Options

A. The pH may increase or decrease
B. All the salts, except those of a strong acid and a strong base undergoes hydrolysis
C. The variation of pH depends upon the nature of the salt as well on temperature
D. All of these

Answer

### Step-by-Step Solution:

1. **Understanding Hydrolysis**: Hydrolysis is the interaction of anions and cations from an electrolyte with the H⁺ and OH⁻ ions present in water, which results in the production of acidity or alkalinity in the solution.

2. **Role of pH**: The pH of a solution is defined as pH = -log[H⁺]. A lower pH indicates a higher concentration of H⁺ ions, which corresponds to an acidic solution, while a higher pH indicates a lower concentration of H⁺ ions, corresponding to a basic solution.

3. **Hydrolysis of Salts**: Not all salts undergo hydrolysis. Strong acids and strong bases do not undergo hydrolysis because they completely dissociate in water. For example, when NaCl (a salt formed from a strong acid and a strong base) is dissolved in water, it dissociates into Na⁺ and Cl⁻ ions, which do not affect the pH significantly.

4. **Examples of Hydrolysis**: Consider NH₄Cl, which is formed from a weak base (NH₄OH) and a strong acid (HCl). When NH₄Cl is dissolved in water, it undergoes hydrolysis:
- NH₄⁺ + H₂O ⇌ NH₃ + H₃O⁺
This increases the concentration of H₃O⁺ ions, lowering the pH and making the solution acidic.

5. **Effect of Temperature on pH**: The pH of a solution can also be affected by temperature. As temperature increases, the kinetic energy of the molecules increases, which can affect the dissociation of water and the equilibrium of hydrolysis reactions. Generally, an increase in temperature can lead to a decrease in pH due to increased ionization.

6. **Conclusion**: Based on the above points, we can conclude that:
- Hydrolysis occurs for salts derived from weak acids and bases.
- The pH of a solution depends on the nature of the salt and the temperature.
- All four statements regarding hydrolysis and its effects are correct.