An element $A$ burns with a golden yellow flame in air. It reacts with another element $B$ (atomic number $17$) to give a product $C$. An aqueous solution of product $C$ on electrolysis gives a compound $D$ and liberates hydrogen. Identify $A$,$B$,$C$,and $D$. Also,write down the equations for the reactions involved.

Which kind of impurities are present in the ores? What are these impurities collectively known as?

Give the formulae of the stable binary compounds that would be formed by the combination of the following pairs of elements:
$(a)$ $Mg$ and $N_{2}$
$(b)$ $Li$ and $O_{2}$
$(c)$ $Al$ and $Cl_{2}$
$(d)$ $K$ and $O_{2}$

Why is iron galvanised with zinc? Can it be galvanised with copper? If not,why?

During the extraction of metals,electrolytic refining is used to obtain pure metals.
$(a)$ Which material will be used as the anode and cathode for the refining of silver metal by this process?
$(b)$ Suggest a suitable electrolyte as well.
$(c)$ In this electrolytic cell,where do we get pure silver after passing an electric current?

When an aqueous solution of ammonia is added to an aqueous solution of cupric sulfate,which substance forms a pale blue precipitate?