`B(OH)_(3)+NaOH to Na[B(OH)_(4)](aq).`
Then addition of which of the following shifts the reaction in the backward direction.

Options

A. Cis-`1,2` diol
B. Trans `1,2` diol
C. Borax
D. `Na_(2)HPO_(4)`

Answer

A

Explanation

If certain organic polyhydroxy compounds such as glycerol, manitol or sugars are added to the titration mixture, then `B(OH)_(3)` behaves as a strong monobasic acid and it can be now titrated with `NaOH` and the end point is detected using phenolphthalein as indicator `(pH=8.3-10.0)`.
The added compound must be a cis-diol, to enhance the acid properties.The cis-diol forms very stable complex with the `[B(OH)_(4)]^(-)`, thus removing it from solution.The reaction is reversible and thus removal of one of the products swift the equilibrium in the forward direction and thus all the `B(OH)_(3)` reacts with `NaOH`, in effect it acts as a strong acid in the presence of the cis-diol.
`B(OH)_(3)+NaOH to Na[B(OH)_(4)]+NaBO_(2)+2H_(2)O`.