Which of the following ions will not give a precipitate with $AgNO_3$?

$X$ (salt) + $AgNO_3$ $(aq.) \to \underset{(\text{Yellow ppt.})}{Y \downarrow}$ (soluble in excess of $NH_3$ solution). Salt $X$ does not contain:

$A$ substance reacts with dilute $H_2SO_4$ to release a colorless gas,which turns baryta water $[Ba(OH)_2]$ turbid and decolorizes an acidic solution of dichromate. The presence of which of the following is indicated by this reaction?

When $BaCl_2$ is added to a clear solution of compound $(X)$,a heavy white precipitate is formed,which is insoluble in dilute $HCl$. What is compound $(X)$?

How do you account for the following observations?
$(a)$ Though alkaline potassium permanganate and acidic potassium permanganate both are used as oxidants,yet in the manufacture of benzoic acid from toluene,we use alcoholic potassium permanganate as an oxidant. Why? Write a balanced redox equation for the reaction.
$(b)$ When concentrated sulphuric acid is added to an inorganic mixture containing chloride,we get a colourless pungent-smelling gas $HCl$,but if the mixture contains bromide,then we get red vapours of bromine. Why?

$A$ white sodium salt dissolves readily in water to give a solution which is neutral to litmus. When silver nitrate solution is added to the aforementioned solution,a white precipitate is obtained which does not dissolve in dilute nitric acid. The anion is: