The correct option is
D The titration is an example of titration of mixture of acids against strong base
(NaOH).
When mixture of acid is titrated with
NaOH, strong acid will react first followed by weak acid.
Here,
HCl will react with
NaOH in the start and get neutralised.
The neutralised reaction is,
HCl+NaOH→NaCl+H2O
During this reaction, the conductance of the solution gradually decreases due to the removal of
H+ ions of highly ionised
HCl to form unionised water. This will be the first
part of the graph.
When
HCl is finished
HCN starts reacting with
NaOH.
Here, the neutralisation reaction is
HCN+NaOH→NaCN+H2O
During the neutralisation of weak acid the conductance increases marginally due to the salts
(NaCN) produced which will be the second part of graph.
After the equivalence point, the increase in conductance is appreciable due to the added
OH− ions.
Thus, the conductance will decrease steeply and then increase marginally and again increase steeply.
Thus, option (d) is correct.