In the qualitative analysis of nitrate,a brown ring is formed due to the formation of:

Which of the following radicals does not liberate gas with ($Zn$ + dil. $HCl$) on warming?

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.

The phosphate radical reacts with ammonium molybdate to form a precipitate of which color?

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:

The brown ring test is used to detect the presence of which ion?