A white powder solid A forms a light green solution with water, which one treatment with potassium hexacyanoferrate (III) gives a blue precipitate. On being strongly heated. A leaves a brown residue and forms a mixture off two gaseous oxides, which turns a dichromate solution green and forms a white precipitate with a `BaCl_(2)` solutio containing concentrated HCl. A is:

Options

A. `CuSO_(4)`
B. `Fe_(2)(SO_(4))_(3)`
C. `FeSO_(4)`
D. `Cr_(2)(SO_(4))_(3)`

Answer

To solve the problem, we need to analyze the given information step by step.

### Step 1: Identify the nature of solid A
The question states that solid A is a white powder that forms a light green solution with water. This indicates that A is likely a ferrous compound, as ferrous ions (Fe²⁺) can impart a light green color to a solution.

**Hint:** Look for ferrous compounds that are white solids and can dissolve in water to give a colored solution.

### Step 2: Reaction with potassium hexacyanoferrate (III)
When solid A is treated with potassium hexacyanoferrate (III), it produces a blue precipitate. The blue precipitate formed in this reaction is known as Prussian blue, which is indicative of the presence of ferrous ions (Fe²⁺).

**Hint:** Recall that the formation of Prussian blue is a characteristic reaction of ferrous ions with potassium hexacyanoferrate (III).

### Step 3: Heating solid A
Upon strong heating, solid A leaves a brown residue and produces two gaseous oxides. The brown residue suggests the formation of ferric oxide (Fe₂O₃), which is consistent with the decomposition of ferrous sulfate (FeSO₄). The gases produced are likely sulfur dioxide (SO₂) and sulfur trioxide (SO₃), which are also products of the decomposition of iron(II) sulfate.

**Hint:** Consider the thermal decomposition of iron(II) sulfate and the gases it produces.

### Step 4: Reaction with dichromate solution
The question mentions that the gaseous products turn a dichromate solution green. This indicates that one of the gases, likely SO₂, is reducing the dichromate (Cr₂O₇²⁻) to chromium(III) ions (Cr³⁺), which are green in color.

**Hint:** Remember that dichromate ions can be reduced to chromium(III) ions by reducing agents like SO₂.

### Step 5: Reaction with BaCl₂ in concentrated HCl
The final piece of information states that a white precipitate is formed when the gaseous products react with BaCl₂ in concentrated HCl. This white precipitate is likely barium sulfate (BaSO₄), which forms when sulfate ions (from SO₃) react with barium ions.

**Hint:** Think about the formation of precipitates in reactions involving sulfate ions and barium ions.

### Conclusion
Based on the analysis of all the steps, we can conclude that solid A is **ferrous sulfate (FeSO₄)**. It meets all the criteria outlined in the question.

**Final Answer:** A is FeSO₄ (ferrous sulfate).