Given below are two statements :

Statement (I) : The gas liberated on warming a salt with dil $$\mathrm{H}_2 \mathrm{SO}_4$$, turns a piece of paper dipped in lead acetate into black, it is a confirmatory test for sulphide ion.

Statement (II) : In statement-I the colour of paper turns black because of formation of lead sulphite. In the light of the above statements, choose the most appropriate answer from the options given below :

The final product A, formed in the following multistep reaction sequence is :

This reduction reaction is known as:

Compound A formed in the following reaction reacts with B gives the product C. Find out A and B.