Which of the following reagents would you use to separate $SO_4^{2-}$ ions from a solution containing a mixture of $SO_4^{2-}$ and $Cl^-$ ions?

$A$ mixture when heated with conc. $H_2SO_4$ and $MnO_2$ produces brown fumes due to the presence of:

Which one of the following anions is not easily removed from aqueous solutions by precipitation?

Which of the following substances releases $SO_2$ gas upon reaction with dilute $H_2SO_4$?

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.

Which of the following anions cannot be easily removed from its aqueous solution by precipitation?