Which are buffer mixtures?H3BO3 and boraxNaOH and NaNO3CH3COONa and CH3COOHNH4OH and NH4Cl

Buffer mixtures are solutions that resist changes in pH when small amounts of an acid or a base are added, or when the solution is diluted. They are used to maintain a stable pH in a solution.

1. H3BO3 and Borax: This is not a buffer mixture. Boric acid (H3BO3) is a weak acid, but borax (Na2B4O7.10H2O) is a salt of a strong base and a weak acid. For a buffer solution, you need a weak acid and its conjugate base or a weak base and its conjugate acid.

2. NaOH and NaNO3: This is not a buffer mixture. Sodium hydroxide (NaOH) is a strong base and sodium nitrate (NaNO3) is a salt of a strong acid and a strong base. Neither of these combinations can act as a buffer.

3. CH3COONa and CH3COOH: This is a buffer mixture. Acetic acid (CH3COOH) is a weak acid and sodium acetate (CH3COONa) is its conjugate base. This combination can resist changes in pH, so it acts as a buffer.

4. NH4OH and NH4Cl: This is a buffer mixture. Ammonium hydroxide (NH4OH) is a weak base and ammonium chloride (NH4Cl) is its conjugate acid. This combination can resist changes in pH, so it acts as a buffer.