Answer : The good buffer systems are, (a), (b), (c) and (e)
Explanation :
Buffer : It is a solution that prevent any changes in the pH of the solution on the addition of an acidic and basic components.
Or, it is a solution that maintain the pH of the solution by adding the small amount of acid or a base.
There are two types of buffer which are acidic buffer and basic buffer.
Acidic buffer : It is the solution that have the pH less than 7 and it contains weak acid and its salt. For example : Acetic acid (weak acid) and sodium acetate (salt).
Basic buffer : It is the solution that have the pH more than 7 and it contains weak base and its salt. For example : Ammonia (weak base) and ammonium chloride (salt).
The conditions for a good buffer system is:
(1) a weak acid and its conjugate base.
(2) a weak base and its conjugate acid.
(a) 0.37 M hydrocyanic acid + 0.24 M sodium cyanide
It is a combination of weak acid and its conjugate base. So, it is a good buffer.
(b) 0.14 M sodium nitrite + 0.27 M nitrous acid
It is a combination of weak acid and its conjugate base. So, it is a good buffer.
(c) 0.21 M hypochlorous acid + 0.13 M potassium hypochlorite
It is a combination of weak acid and its conjugate base. So, it is a good buffer.
(d) 0.20 M nitric acid + 0.22 M potassium nitrate
It is a combination of strong acid. So, it will not form buffer solution.
(e) 0.32 M ammonium bromide + 0.31 M ammonia
It is a combination of weak base and its conjugate acid. So, it is a good buffer.
Hence, the good buffer systems are, (a), (b), (c) and (e)