Question

Identify correct statements from the following:
i. $H _{3} BO _{3}$ is a monobasic acid.
ii. The correct formula of borax is $Na _{2}\left[ B _{4} O _{5}( OH )_{3}\right] 8 H _{2} O$
iii. $NaBH _{4}$ is a reducing agent

• A. i, ii, iii
• B. i, ii only
• C. ii, iii only
• D. i, iii only

Answer 1

Answer: (D)

The explanations of given statements are as follows:

(i) $H _{3} BO _{3}$ is a monobasic acid because in aqueous solution, it coordinates with a molecule of water to form a hydrated species,

$B ^{3+}$ ion pulls the $\sigma$ -electron charge of coordinated O-atom towards itself. The coordinated oxygen, in turn, pull the $\sigma$ -electrons of $O - H$ bond of the attached water molecule towards itself. This facilitates the removal of $H ^{+}$ ion from the O- $H$ bond

It can be written as follows:

$B ( OH )_{3}+ H _{2} O \rightleftharpoons\left[ B ( OH )_{4}\right]^{-}+ H ^{+}$

(ii) The correct formula for borax is $Na _{2}\left[ B _{4} O _{7}\right] \cdot 10 H _{2} O$

(iii) $NaBH _{4}$ is a selective reducing agent for aldehydes, ketones and ester.

Thus, statements (i) and (iii) are correct