A mixture consists of A (yellow solid) and B (colourless solid) which gives filac colour in flame.
a. The mixture gives black precipitate C on passing `H_(2)S` gas
b. C is soluble in aqua and on evaportation of aquaregain and adding `SnCI_(2)` gives greyish -black precipitate D
c. The salt solution with `NH_(4)OH` gives a brown precipitate .
i. The sodium extract of the salt with `C CI_(4)//FeCI_(3) AgNO_(2)` solution which is insoluble in `NH_(3)`
Identify A and B and the precipitate C and D

Explanation

`A: KI,B : HGI_(2) , C : HgS , D : Hg`
A mixture consists of a (yellow solid ) and B (colourless solid) which gives lilac colour in flame lilac colour come from piotassium ions . Mixture gives black precipitate C on passing `H_(2)S` gas C is soluble in aqua regain it must be HgS .On eveoration of aqua regain and adding `SnCI_(2)` it give a greyish-black precipitate D .This must be mercury .The salt solution with `NH_(4)OH` gives a brown precipitate .it must be iodide of Millon's base mercuric iodide .The sodium extract of the salt with `C CI_(4)//FeCI_(3)` gives a violet layer .This conform iodide .The sodium extract gives a yellow precipitate with `AgNO_(3)` solution which is insoloble in `NH_(3)` This also conform iodide
`HgI_(2) + H_(2)S rarr underset(Black)(HgS darr )+ 2HI`
`HgS overset("Aqua regia")rarr HgCI_(2)` (Soluble)
`HgCI_(2) overset(SnCI)rarr SnCI_(4) +underset(Black)(Hg)` ltbr? `2KI +HgI_(2) rarr underset("Nessler's reagent")(K_(2)HgI_(4))`
`K_(2)HgI_(4) overset(NH_(3))rarr underset("Iodide of million's base")(H_(2)N-Hg-O-Hg-I)`
With sodium extract:
`2NaI +2Fe^(3+) overset( C CI_(4))rarr I_(2) +2Na^(o+) +Fe^(2+)`
`AgNO_(3) +NaI rarr AGi darr + NaNO_(3)`
`AgI` is the yellow precipitate insoluble in ammonium hydroxide.