Which reagent below would enable you to remove sulphate ions from a solution containing both sulphate and chloride ions?

Which anion of a sodium salt gives a white precipitate upon heating with a magnesium salt?

$A$ salt is heated first with dil. $H_2SO_4$ and then with conc. $H_2SO_4$. No reaction takes place. It may be

Assertion $(A) :- Fe^{+3}$ is not used in the brown ring test for $NO_3^{-}$.
Reason $(R) :-$ Reduction of $NO_3^{-}$ takes place during the test.

Given below are two statements:
Statement-$I$: The gas liberated on warming a salt with dil $H_2SO_4$,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:

$A$ sodium salt on treatment with $MgCl_2$ gives white precipitate only on heating. The anion of the sodium salt is