A white powder "A" on heating gave a non-combustible gas and a white residue. The residue on heating turns yellow. The residue dissolves in dil. HCl and the solution gives a white ppt. with `K_(4)[Fe(CN)_(6)]`. "A" would be:

Options

A. `CaCO_(3)`
B. `ZnCO_(3)`
C. `CaSO_3`
D. `CuCO_(3)`

Answer

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

### Step 1: Identify the characteristics of the white powder "A"
The question states that "A" is a white powder that, upon heating, produces a non-combustible gas and a white residue.

**Hint:** Consider common white powders that can release gases upon heating.

### Step 2: Determine the non-combustible gas produced
When the white powder is heated, it produces a non-combustible gas. Common non-combustible gases include carbon dioxide (CO₂), which is often released when carbonates decompose.

**Hint:** Think about which white powders are carbonates that release CO₂ upon heating.

### Step 3: Identify the white residue
The residue left after heating is white and, upon further heating, turns yellow. This property is characteristic of zinc oxide (ZnO), which is white when cold and turns yellow when heated.

**Hint:** Recall the thermal properties of metal oxides, particularly zinc oxide.

### Step 4: Confirm the identity of the white powder "A"
Since the residue is zinc oxide, the original white powder "A" must be zinc carbonate (ZnCO₃), which decomposes upon heating to form zinc oxide and carbon dioxide:
\[ \text{ZnCO}_3 (s) \rightarrow \text{ZnO} (s) + \text{CO}_2 (g) \]

**Hint:** Look for the decomposition reaction of zinc carbonate.

### Step 5: Analyze the behavior of the residue in dilute HCl
The white residue (ZnO) dissolves in dilute hydrochloric acid (HCl) to form zinc chloride (ZnCl₂):
\[ \text{ZnO} (s) + 2 \text{HCl} (aq) \rightarrow \text{ZnCl}_2 (aq) + \text{H}_2\text{O} (l) \]

**Hint:** Consider the solubility of metal oxides in acids.

### Step 6: Identify the precipitate formed with K₄[Fe(CN)₆]
When zinc chloride (ZnCl₂) reacts with potassium ferrocyanide (K₄[Fe(CN)₆]), it forms a white precipitate of zinc ferrocyanide:
\[ \text{ZnCl}_2 (aq) + K_4[\text{Fe(CN)}_6] (aq) \rightarrow \text{Zn}_2[\text{Fe(CN)}_6] (s) + 2 \text{KCl} (aq) \]

**Hint:** Remember that certain metal ions form colored or white precipitates with ferrocyanides.

### Conclusion
Based on the analysis, the white powder "A" is identified as zinc carbonate (ZnCO₃).

**Final Answer:** The white powder "A" would be zinc carbonate (ZnCO₃).