Using a single reagent, how could I discern between the following substances? In other words, what single reagent would precipitate one while not the other?

Question

anonymous · Answer

$$Hg_2(NO_3)_2 \ and \ Hg(NO3)_2$$

apoorvk · Answer

the first one has Hg(I) and the second one contains Hg(II) by valency. Now in the groupings of basic radicals, Hg(I) lies in the 1st group, whose group reagent for identification is dil. HCl, and Hg(II) lies in the second group whose group reagent is dil HCl, followed by dihydrogen sulphide gas (H2S) being passed into the mixture of the gas.
Ofcourse, nitrate ions are common to both.

So, using HCl as a reagent we can determine which compound is from which group. The one which gives a reaction to HCl simply, will be the first one, and the other is not.