The correct option (a) Addition of cis 1, 2 diol
Explanation:
B(OH)3 + NaOH ⇋ NaBO2 + Na[B(OH)4] + H2O
This reaction is reversible reaction because sodium metaborate, Na+[B(OH)4]- formed by the reaction between B(OH)3 and NaOH gets hydrolysed to regenerate B(OH)3 and NaOH
If, some quantity of polyhydroxy compounds like cis- 1, 2-diol, catechol, glycerol etc is added to the reaction mixture then the B(OH)3 combines with such polyhydroxy compounds to give chelated complex compound. Due to complex compound formation, stability increases and due to higher stability of complex, reaction moves in forward direction.