Which of the following halides react$(s)$ with $AgNO_{3(aq)}$ to give a precipitate that dissolves in $Na_2S_2O_{3(aq)}$?
$A$. $HCl$
$B$. $HF$
$C$. $HBr$
$D$. $HI$

Match List-$I$ with List-$II$:

List-$I$ (Anion)	List-$II$ (Gas evolved on reaction with dil. $H_2SO_4$)
$A. CO_3^{2-}$	$I$. Colourless gas which turns lead acetate paper black
$B. S^{2-}$	$II$. Colourless gas which turns acidified potassium dichromate solution green
$C. SO_3^{2-}$	$III$. Brown fumes which turn acidified $KI$ solution containing starch blue
$D. NO_2^{-}$	$IV$. Colourless gas evolved with brisk effervescence,which turns lime water milky

Choose the correct answer from the options given below:

An unknown salt (anion) reacts with dilute $HCl$ to produce gas $X$ (rotten egg smell). Choose the incorrect option regarding gas $X$.

$A$ brown ring appears in the test for

Why is it necessary to use acetic acid and not sulphuric acid for acidification of sodium extract for testing sulphur by lead acetate test?

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 $g \ mol^{-1}$: $Na: 23$,$N: 14$,$K: 39$,$O: 16$,$Br: 80$,$I: 127$,$F: 19$,$Ca: 40$)