The most efficient agent for the absorption of $SO_3$ is

Sulphur dioxide reacts with chlorine in the presence of charcoal to give

$A$ sulphate of a metal $(A)$ on heating evolves two gases $(B)$ and $(C)$ and an oxide $(D).$ Gas $(B)$ turns $K_2Cr_2O_7$ paper green while gas $(C)$ forms a trimer in which there is no $S-S$ bond. Compound $(D)$ with $HCl$ reacts to form a compound $(E)$ which exists as a dimer. Compounds $(A)$,$(B)$,$(C)$,$(D)$ and $(E)$ are respectively:

Identify the method used to obtain $SO_2$ gas in industry.

Which one of the following is the correct decreasing order of boiling point?

Provide information regarding the ionization enthalpy,electron gain enthalpy,and electronegativity of the elements of Group-$16$.