(b) Compound A is used in the manufacture of optical. A on heating gives B. B further heating to form C. A reacts with hydrochloric acid to give D. Identify A, B,C and D. Explain the reaction.

Explanation

(i) Compound (A) is borax, which is used in the manufacture of opticals.
(ii) Borax(A) on heating to give borax glass (B). Borax glass on further heating to give sodium metaborate (C).
`underset(("Borax"))(Na_(2)B_(4)O_(7)).10H_(2)Ounderset(-10H_(2)O)overset(Delta)(to)underset((B))underset(("Borax glass"))(Na_(2)B_(4)O_(7))overset(Delta)(to)underset((C))underset(("Sodium metaborate"))(2NaBO_(2))+B_(2)O_(3)`
(iii) Borax (A) reacts with hydrochloride acid to give boric acid.
`underset((A))underset(("Borax"))(Na_(2)B_(4)O_(7))+2HCl+7H_(2)otounderset((D))underset(("Boric acid"))(4H_(3)BO_(3))+2NaCl`