A buffer has a maximum buffer capacity when the ratio of salt to acid is:
A.10
B.2
C.4
D.1

Hint: Buffer capacity is quantitative and is defined as the resistance of the solution containing the buffering agent to change its pH when the concentration of acid or alkali changes.

Complete step by step answer:
At certain times it is required to maintain the pH value of any solution and hence the weak acid or base is used to maintain the acidity of the solution around the desired value. This weak acid or base is known as Buffering agent. Some of the examples of buffering agents are carbonates, bicarbonates, formic acid, fumaric acid, etc. The measure of the efficiency of a buffer in resisting pH changes is known as Buffer Capacity (β). It is mathematically expressed are:
$\beta = \dfrac{{\Delta B}}{{\Delta pH}}$,
Here, $\Delta B$is defined as the number of moles of an acid or base required to change the value of pH by 1 for 1 litre, and $\Delta pH$ is defined as the change in pH due to the addition of acid or base. Buffer capacity is a unitless quantity and is dependent on two factors:
The ratio of salt and base
Total buffer capacity.
Hence for the buffer capacity to be maximum, the ratio of salt and base should be in the ratio 1:1.



Note:
Buffer capacity for a weak acid with a dissociation constant as $K_a$ is defined mathematically as:
$\beta = 2.303\left( {[{H^ + }] + \dfrac{{{T_{HA}}{K_a}[{H^ + }]}}{{{{({K_a} + [{H^ + }])}^2}}} + \dfrac{{{K_w}}}{{[{H^ + }]}}} \right)$
Here, the concentration of hydrogen ions is expressed by $[{H^ + }]$ and the total added acid is expressed by \[{T_{HA}}\]. With reference to the above formula, in the case of strong acidic solution (pH < 2), buffer capacity rises exponentially with a decrease in pH and for the case of strong alkaline solution (pH > 12), buffer capacity rises exponentially with an increase in pH.