91Ó°ÊÓ

Amorphous boron is extracted from borax by following steps: \(\operatorname{Borax} \stackrel{(A)}{\longrightarrow} \mathrm{H}_{3} \mathrm{BO}_{3} \stackrel{(B)}{\longrightarrow} \mathrm{B}_{2} \mathrm{O}_{3} \stackrel{(C)}{\longrightarrow}\) Boron (A) and \((C)\) are : (a) \(\mathrm{H}_{2} \mathrm{SO}_{4}, \mathrm{Al}\) (b) \(\mathrm{HCl}, \mathrm{C}\) (c) \(\mathrm{HCl}, \mathrm{Fe}\) (d) \(\mathrm{H}_{2} \mathrm{SO}_{4}, \mathrm{Na}\)

Which acids are formed by the action of water on phosphorus pentoxide ? (a) \(\mathrm{HPO}_{3}\) (b) \(\mathrm{H}_{4} \mathrm{P}_{2} \mathrm{O}_{7}\) (c) \(\mathrm{H}_{3} \mathrm{PO}_{4}\) (d) \(\mathrm{H}_{3} \mathrm{PO}_{3}\)

Which of the following statements are correct? (a) \(\mathrm{Cl}_{2}\) reacts with aqueous \(\mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}\) to form \(\mathrm{HCl}\) and \(\mathrm{NaHSO}_{4}\) (b) \(\mathrm{Cl}_{2}\) reacts with aqueous \(\mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}\) to give \(\mathrm{Na}_{2} \mathrm{~S}_{4} \mathrm{O}_{6}\) and \(\mathrm{NaCl}\) (c) A white precipitate of silver thiosulphate is formed which changes to yellow, brown and finally black when silver nitrate is added to \(\mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}\). (d) Sodium thiosulphate is quantitatively oxidised by iodine.

(A) All the oxidation states of nitrogen from \(+1\) to \(+4\) show disproportionation in acidic medium. (R) Aqueous nitric acid undergoes disproportionation.

The general formula of cyclic or ring silicates is : (a) \(\left(\mathrm{Si}_{2} \mathrm{O}_{5}\right)_{n}^{2 n-}\) (b) \(\left(\mathrm{SiO}_{3}\right)_{n}^{2 n-}\) (c) \(\left(\mathrm{SiO}_{3}^{2}\right)_{n}\) (d) both (b) and (c)