When a white crystalline compound X is heated with `K_(2)Cr_(2)O_(7)` and concentrated `H_(2)SO_(4)` a reddish brown gas A is evolved. On passing A into caustic soda solution, a yellow 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_2HgI_4` solution, a reddish brown precipitate D is formed. Identify A, B, C, D and X. Write the equations of reactions involved.

Explanation

To solve the problem step by step, we need to identify the compounds A, B, C, D, and X based on the reactions described in the question.

### Step 1: Identify Compound X
The question states that a white crystalline compound X is heated with potassium dichromate (K₂Cr₂O₇) and concentrated sulfuric acid (H₂SO₄). The most likely candidate for X is **ammonium chloride (NH₄Cl)**, as it is a white crystalline solid.

### Step 2: Reaction of X with K₂Cr₂O₇ and H₂SO₄
When ammonium chloride (X) is heated with K₂Cr₂O₇ and concentrated H₂SO₄, the following reaction occurs:
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