$A$ solution of a salt in dilute sulphuric acid imparts a deep blue colour with starch-iodine solution; it confirms the presence of which of the following?

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

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.

Sodium salt solution $+ \, AgNO_3$ solution $\to$ Coloured precipitate: If the coloured precipitate is soluble in both dilute $HNO_3$ and excess concentrated $NH_3$ solution,then which of the following anions is present in the salt solution?

Molar mass of the salt from $NaBr$,$NaNO_3$,$KI$,and $CaF_2$ which does not evolve coloured vapours on heating with concentrated $H_2SO_4$ is . . . . . . $g \ mol^{-1}$. (Molar mass in $g \ mol^{-1}$: $Na: 23$,$N: 14$,$K: 39$,$O: 16$,$Br: 80$,$I: 127$,$F: 19$,$Ca: 40$)

Formation of $Na_4[Fe(CN)_5NOS]$,a purple coloured complex formed by addition of sodium nitroprusside in sodium carbonate extract of salt indicates the presence of $:$