Potassium dichromate is prepared from

Options

A. chromate obtined by the fusion of chromite ore with sodium carbonate in free access of air
B. pyrolusite which is fused with potassium hydroxide in th presence of air
C. iron pyrites by the fusion with potassium carbonate in presence of moisture
D. none of these

Explanation

To prepare potassium dichromate, we can follow these steps:

### Step 1: Understand the Source Material
Potassium dichromate (K2Cr2O7) is derived from chromate. The chromate is obtained from chromite ore (FeCr2O4).

**Hint:** Identify the ore that contains chromium, which is essential for preparing chromate.

### Step 2: Reaction with Sodium Carbonate
The first step involves the fusion of chromite ore with sodium carbonate (Na2CO3) in the presence of excess oxygen (O2). The reaction can be represented as follows:

\[ \text{FeCr}_2\text{O}_4 + \text{Na}_2\text{CO}_3 + 9\text{O}_2 \rightarrow \text{NaCrO}_4 + 2\text{Fe}_2\text{O}_3 + 4\text{CO}_2 \]

In this reaction, sodium chromate (Na2CrO4) is produced.

**Hint:** Remember that the presence of oxygen is crucial in this step for converting chromite to chromate.

### Step 3: Conversion to Sodium Dichromate
Next, sodium chromate can be converted to sodium dichromate (Na2Cr2O7) through a reaction with water and hydrochloric acid (HCl). The reaction can be represented as:

\[ \text{Na}_2\text{CrO}_4 + \text{H}_2\text{O} + \text{HCl} \rightarrow \text{Na}_2\text{Cr}_2\text{O}_7 + \text{NaCl} + \text{H}_2\text{O} \]

**Hint:** This step involves the transformation of chromate into dichromate, which is a common reaction in inorganic chemistry.

### Step 4: Final Reaction to Form Potassium Dichromate
Finally, sodium dichromate can be reacted with potassium chloride (KCl) to yield potassium dichromate:

\[ \text{Na}_2\text{Cr}_2\text{O}_7 + 2\text{KCl} \rightarrow 2\text{K}_2\text{Cr}_2\text{O}_7 + \text{NaCl} \]

This reaction results in the formation of potassium dichromate.

**Hint:** This step involves a double displacement reaction where sodium is replaced by potassium.

### Conclusion
Thus, potassium dichromate is prepared from chromate obtained by the fusion of chromite ore with sodium carbonate in the presence of excess air.

**Final Answer:** The correct option is (A) chromate obtained by the fusion of chromite ore with sodium carbonate in free access of air.