Buffer Solution:
A buffer solution is a solution that resists changes in pH when small amounts of acid or base are added to it. It contains a weak acid and its conjugate base or a weak base and its conjugate acid. The buffer solution maintains the pH by neutralizing the added acid or base through the reaction between the weak acid and its conjugate base, or the weak base and its conjugate acid.

Options for Preparing Buffer Solution:
a) Sodium acetate and acetic acid in water
c) Ammonia and ammonium chloride in water

Explanation:
a) Sodium acetate and acetic acid in water:
- Acetic acid is a weak acid and sodium acetate is its conjugate base.
- When acetic acid is dissolved in water, it partially dissociates into hydrogen ions (H+) and acetate ions (CH3COO-).
- Sodium acetate dissociates completely into sodium ions (Na+) and acetate ions (CH3COO-) in water.
- The acetate ions from sodium acetate react with the hydrogen ions from acetic acid to form undissociated acetic acid, maintaining the pH of the solution.
- This combination of acetic acid and sodium acetate forms a buffer solution.

c) Ammonia and ammonium chloride in water:
- Ammonia is a weak base and ammonium chloride is its conjugate acid.
- Ammonium chloride dissociates into ammonium ions (NH4+) and chloride ions (Cl-) in water.
- Ammonia accepts a hydrogen ion from water to form ammonium ions and hydroxide ions (OH-).
- The hydroxide ions react with the hydrogen ions from ammonium chloride to form water, maintaining the pH of the solution.
- This combination of ammonia and ammonium chloride forms a buffer solution.

Conclusion:
A buffer solution can be prepared from a mixture of sodium acetate and acetic acid in water or from a mixture of ammonia and ammonium chloride in water. These combinations provide a weak acid and its conjugate base or a weak base and its conjugate acid, which can neutralize added acid or base and maintain the pH of the solution.

Yes the answer is right because in the option A,C there is a common ion which is essential for the preparation of buffer solution so A,C is crt