Which salt produces a white precipitate with $AgNO_3$ solution,which becomes black on standing?

What is the color of the precipitate formed when phosphate ions react with ammonium molybdate?

$A$ substance reacts with dilute $H_2SO_4$ to release a colorless gas,which turns baryta water $[Ba(OH)_2]$ turbid and decolorizes an acidic solution of dichromate. The presence of which of the following is indicated by this reaction?

Which of the following gives a precipitate with $Pb(NO_3)_2$ but not with $Ba(NO_3)_2$?

When a solution of a mixture having two inorganic salts was treated with freshly prepared ferrous sulphate in an acidic medium,a dark brown ring was formed,whereas on treatment with neutral $FeCl_3$,it gave a deep red colour which disappeared on boiling and a brown-red precipitate was formed. The mixture contains:

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 $:$