Name the kind of silicate formed when two silicate units $(SiO_4)^{4-}$ share one oxygen atom.

Which one of the following is a correct set?

$A$ thin layer of aluminum deposited on glass acts as a good mirror because ...............

$A$ gas that cannot be collected over water is

Which of the following oxides is amphoteric?

Find $A$,$B$ and $C$ in the following reactions:
$NH_3 + A + CO_2 \rightarrow (NH_4)_2CO_3$
$(NH_4)_2CO_3 + H_2O + B \rightarrow 2NH_4HCO_3$
$NH_4HCO_3 + NaCl \rightarrow NH_4Cl + C$