Which of the following aqueous solutions are good buffer systems? . 0.11 m sodium hydroxide + 0.30 m sodium bromide 0.33 m potassium chloride + 0.20 m calcium chloride 0.28 m nitric acid + 0.23 m sodium nitrate 0.31 m ammonia + 0.31 m calcium hydroxide 0.21 m hydrofluoric acid + 0.20 m potassium fluoride

Buffer is composed of weak acid and its conjugate base or weak base and it is conjugate acid. so The correct answer is:
0.21 M hydrofluoric acid + 0.20 M potassium Fluoride
due to the first choice contain NaOH which is strong base not weak
second choice both salts no acid or base
Third choice contain HNO₃ which is considered as strong acid
Fourth choice contain ammonia but without its conjugate acid like (NH₄Cl for example) instead it has different salt
Fifth Choice contain HF which is weak acid and KF which is its conjugate base so this is the correct one

Putting salt in vinegar water

Ansaquatic plants;