Identify `(A)` to `( E)`.
(a) An inorganic iodide `(A)` on heating with a solution of `KOH` gives a gas `(B)` and the solution of a compound `( C)`.
(b) The gas `(B)` on ignition air gives a compound `(D)` and water.
( C) Copper sulphate is reduced to the metal on passing `(B)` through the solution.
(d) A precipitate of the compound `( E)` is formed on reaction of `( C)` with copper sulphate solution.

Explanation

(i) Since element 'A' is a yellow solid in the standard state and forms a foul smelling gas 'B' which is extensively used in qualitative analysis of salts, therefore, the element 'A' must be sulphure `(H_(2)S)`.
`underset(("Yellow solid, A"))underset("Sulphur")(S) + H_(2) overset("Heat")rarr underset(("Foul smelling gas, B"))underset("Hydrogen sulphide")(H_(2)S)`
(ii) Since the volatile gas 'B' reacts with oxygen to form a colourless pungent smelling gas 'C' which decolourises acidified `KMnO_(4)` solution, the gas 'C' must be sulphur dioxide `(SO_(2))`.
`underset("Hydrogen suphide (B)")(2H_(2)S) + 3O_(2) rarr 2 H_(2)O + underset(("Colourless pungent smelling gas C"))underset("Sulphur dioxide")(2SO_(2))`
The gas C being a reducing agent reduces acidified `KMnO_(4)` solution.
`{:(" "2KMnO_(4)+3H_(2)SO_(4) rarr K_(2)SO_(4)+2MnSO_(4)+3H_(2)O+5[O]),(" "SO_(2)+H_(2)O+[O] rarr [H_(2)SO_(4)] xx 5),(bar(underset(("Pink"))(2KMnO_(4))+5SO_(2)+2H_(2)rarr K_(2)SO_(4)+underset(("Colourless"))(2MnSO_(4))+2H_(2)SO_(4))):}`
(iii) Since the colourless pungent smelling gas 'C', i.e., `SO_(2)`, can be oxidised to another oxide 'D' in the presence of a heterogeneous catalyst (i.e., Pt or `V_(2)O_(5)`), therefore, the oxide 'D' must be sulphur trioxide `(SO_(3))`.
`underset("Sulphur dioxide (C)")(2SO_(2)) + O_(2) rarr underset("Sulphur trioxide (D)")(2SO_(3))`
Thus, 'A' is sulphur (S), 'B' is hydrogen sulphide, `(H_(2)S)`. 'C' is sulphur dioxide `(SO_(2))` and 'D' is sulphur trioxide `(SO_(3))`.