When a white crystalline compound X is heated with `K_(2)Cr_(2)O_(7)` and concentrated `H_(2)SO_(4)` a, a reddish brown gas A is evolved. On passing A into caustic soda solutions, a yelow coloured solution of B is obtained. Neutralizing the solution B with acetic acid and on subsequent addition of lead acetate, a yellow precipitate C is obtained.When X is heated with NaOH solution, a colourless gas is evolved and on passing this gas into `K_(2)HgI_(4)` solution, a reddish brown precipitate D is formed. Identify A,B,C,D and X. Write the equation of the reaction involved.

Explanation

The chemical reactions involved are as follows `:`
`4NH_(4)Cl+ K_(2)Cr_(2) O_(7) + 6 H_(2)SO_(4) rarr underset( "Reddish brown")(2CrO_(2)Cl_(2)) + 4NH_(4) HSO_(4) _ 2KHSO_(4) + 3H_(2)O`
`CrO_(2)Cl_(2) + 2NaOH rarr underset("Yellow sol. ")(Na_(2)CrO_(4))+2HCl`
`NH_(4)Cl NaOH rarr NaCl+ NH_(3) + H_(2)O`
`2K_(2)HgI_(4) + NH_(3)+3KOH rarr NH_(2) HgO + 7KI + 2H_(2)O`