A colorless water-soluble compound on strong heating liberates a brown colored gas as one of the products and leaves a residue. An aqueous solution of the original solid gives precipitate with ${(N H_{4})}_{2} S$ and $N H_{4} O H$ . The original solid could be

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$C a {(N O_{3})}_{2}$

$P b {(N O_{3})}_{2}$

$A l {(N O_{3})}_{3}$

$Z n {(N O_{3})}_{2}$

answer is A, B, D.

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Detailed Solution

Chemical Compound Identification Problem

Given Properties:

Colorless, water-soluble compound
On strong heating, liberates a brown colored gas
Leaves a residue after heating
Aqueous solution gives precipitate with (NH₄)₂S and NH₄OH

Find: The identity of the original solid compound

Step 1: Analysis of the Brown Gas

The brown colored gas liberated on heating is characteristic of:

Nitrogen dioxide (NO₂) - brown/reddish-brown gas
This suggests the compound contains nitrate or nitrogen in an oxidized state

Step 2: Analysis of Precipitation Tests

Reagent	Observation	Indicates presence of
(NH₄)₂S	Forms precipitate	Metal ions that form insoluble sulfides
NH₄OH	Forms precipitate	Metal hydroxides or complex formation

Step 3: Thermal Decomposition Analysis

The compound that fits all these criteria is ammonium dichromate:

(NH₄)₂Cr₂O₇ →_Δ Cr₂O₃ + N₂O₄ + 4H₂O

Where:

N₂O₄ ⇌ 2NO₂ (brown gas)
Cr₂O₃ is the green residue left behind

Step 4: Verification of Properties

Property	Ammonium Dichromate	Match
Color	Orange-red crystals, but solutions can appear colorless	✓
Water solubility	Highly soluble	✓
Brown gas on heating	Produces NO₂	✓
Precipitate with reagents	Chromium forms precipitates with both reagents	✓

Final Answer:The original solid compound is ammonium dichromate, (NH₄)₂Cr₂O₇This compound is commonly known for its spectacular "volcano" demonstration in chemistry labs, where it decomposes to form a green residue (Cr₂O₃) and releases brown nitrogen dioxide gas.

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