Which ore is concentrated by the froth flotation process?

In the presence of which catalyst is sulphur dioxide heated at high temperature to form sulphur trioxide?

$A$ metal that exists as a liquid at room temperature is obtained by heating its sulphide in the presence of air. Identify the metal and its ore and give the reaction involved.

Give reasons for the following:
$(i)$ Alloys are used in electrical heating devices rather than pure metals.
$(ii)$ Gold ornaments look new even after several years of use.
$(iii)$ An iron grill should be painted frequently.

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 of the following are not ionic compounds?
$(i)$ $KCl$
$(ii)$ $HCl$
$(iii)$ $CCl_4$
$(iv)$ $NaCl$