The concentration of an acid or base is defined as the ratio of the amount of
O A. solvent to the amount of solute in a solution
O B. conjugate acid to conjugate base
O C. conjugate base to conjugate acid
OD. solute to the amount of solvent in a solution

Option  C

Explanation:

A buffer  aqueous solution  consists of  

a) either a weak acid along with its conjugate base  

b) or a weak base along with its conjugate acid.  

This is used to prevent change in the pH of a solution whenever an acid or a base is added. The pH of a buffer depends upon the ratio of base to acid and this ratio is determined by the Ka value and Henderson-Hasselbalch equation. An ideal buffer has equal amounts of acid and conjugate base

Hence, option C is correct

a:

by the combination of an unlimited number of elements