A colourless solid A on heating gives a white solid B and a colourless gas C, B gives off reddish brown fumes on treatment with dilute acids. On heating with `NH_(4)CI` B gives a colourless gas D and a residue E.
The compound A also gives a colourless gas F on heating with ammonium sulphate and white residue G. Both E and Gimpart bright yellow colour to Bunsen flame. The gas C forms white powder with strongly heated magnesium metal. The white powder forms magnesium hydroxide with water. The gas D, on the other hand, is absorbed by heated calcium which gives of ammonia on hydrolysis. Identify the substances A to G and give reactions for the changes involved.

Explanation

It is advisable to summarize the given facts in the form of a chart.
`underset("Colourless residue")G+underset("Colouress gas")Foverset((NH_(4))_(2)SO_(4))underset(heat)larrunderset("Colourless solid")Aoverset(heat)tounderset("Colourless solid")B+underset("Colourless gas")C`
`underset("Colourless residue")D+underset("Residue")Eoverset(NH_(4)Cl)underset(heat)toBoverset(diL)underset("acid")to`Reddish brown fumes
`underset("Colourless gas")C+"Mg"to"White powder"overset(H_(2)O)toMg(OH)_(2)`
`underset("Colourless gas")D+Ca(heated)overset(H_(2)O)toNH_(3)`
The above reactions lead to the following conclusions.
(a) Gas D. reacts with calcium forming a compound which on hydrolysis gives ammonia indicating that must be nitrogen.
(b) Residues E and G give yellow flame on burning indicating that these are sodium salts. Hence, compounds B (which give E) and A (which give G) must be sodium salts.
(c) The colourless solid B gives reddish brown fumes with dilute acids, the reddish brown sumes are probably of `NO_(2)`. Hence, compound B must be nitrite (recall that `NO_(3)^(-)` ions are not attacked by dil. acids). Consequently. A must be `NO_(3)^(-)` which can give `NO_(2)^(-)` (B) on heating.
Thus, compound A is `NaNO_(3)` which explains all the given reactions as below.
`underset((A))(2NaNO_(3))tounderset((B))(2NaNO_(2))+underset((C))(O_(2)darr)`
(ii) `underset((B))(2NaNO_(2))+H_(2)SO_(4)(dil.)toNa_(2)SO_(4)+2HNO_(2)`
`3HNO_(2)toHNO_(3)+H_(2)O+2NO`
`2NO+O_(2)tounderset("Reddish brown fumes")(2NO_(2)darr)`
(iii) `underset((B))NaNO_(2)+NH_(4)Cloverset(heat)tounderset((E))(NaCl)+underset((D))(N_(2)uarr)+2H_(2)O`
(iv) `underset((A))(2NaNO_(3))+(NH_(4))_(2)SO_(4)tounderset((G))(Na_(2)SO_(4))+underset((F))(2NH_(3))uarr+2NHO_(3)`
(v) `2Mg+underset((C))(O_(2))tounderset("White powder")(2MgO)`
`MgO+H_(2)OtoMg(OH)_(2)`
(vi) `3Ca+underset((D))(N_(2))toCa_(3)N_(2)`
`Ca_(3)N_(2)+6H_(2)Oto3Ca(OH)_(2)+2NH_(3)uarr`
Thus, substance (A) to (G) can be represented as
`A = NaNO_(3)`,`B = NaNO_(2)`,`C = O_(z)`,`D = N_(2)`,E = NaCl,`F = NH_(2)`,`G = Na_(2)SO_(4)`