Which of the following anions does not produce a precipitate with $BaCl_2$ solution,however,gives a precipitate with $AgNO_3$?

$Na_2CO_3$ cannot be used to identify which of the following ions?

Given below are two statements:
Statement $I$: Griess-Ilosvay test is used for the detection of nitrite ion, which involves the use of sulphanilic acid and $\alpha$-naphthylamine reagent.
Statement $II$: In the above test, sulphanilic acid is diazotized by the acidified nitrite ion, which on further coupling with $\alpha$-naphthylamine forms an azo-dye.
In the light of the above statements, choose the correct answer from the options given below.

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?

In the test of sulphate radical,the white precipitate of sulphate is soluble in

When a few drops of $KMnO_4$ are added to an acidic solution of an anion,which of the following,if present,will $NOT$ decolorize $KMnO_4$?