Find the number of compounds which have yellow colour ppt from the given compounds :
`Ag_(2)CrO_(4),PbCrO_(4),Hg_(2)CrO_(4),BaCrO_(4)`

Explanation

To determine the number of compounds that yield a yellow color precipitate from the given compounds: \( \text{Ag}_2\text{CrO}_4, \text{PbCrO}_4, \text{Hg}_2\text{CrO}_4, \text{BaCrO}_4 \), we will analyze each compound one by one.

### Step 1: Analyze \( \text{Ag}_2\text{CrO}_4 \)
- When silver nitrate (\( \text{AgNO}_3 \)) reacts with potassium chromate (\( \text{K}_2\text{CrO}_4 \)), it forms silver chromate (\( \text{Ag}_2\text{CrO}_4 \)) and potassium nitrate (\( \text{KNO}_3 \)).
- The precipitate formed is described as brown-red.

**Conclusion**: \( \text{Ag}_2\text{CrO}_4 \) does not yield a yellow precipitate.

### Step 2: Analyze \( \text{PbCrO}_4 \)
- Lead(II) acetate (\( \text{Pb(CH}_3\text{COO)}_2 \)) reacts with sodium chromate (\( \text{Na}_2\text{CrO}_4 \)) to form lead chromate (\( \text{PbCrO}_4 \)) and sodium acetate (\( \text{NaCH}_3\text{COO} \)).
- The precipitate formed is yellow.

**Conclusion**: \( \text{PbCrO}_4 \) yields a yellow precipitate.

### Step 3: Analyze \( \text{Hg}_2\text{CrO}_4 \)
- Mercury(I) chromate (\( \text{Hg}_2\text{CrO}_4 \)) is known to form a red precipitate.

**Conclusion**: \( \text{Hg}_2\text{CrO}_4 \) does not yield a yellow precipitate.

### Step 4: Analyze \( \text{BaCrO}_4 \)
- Barium hydroxide (\( \text{Ba(OH)}_2 \)) reacts with potassium dichromate (\( \text{K}_2\text{Cr}_2\text{O}_7 \)) to form barium chromate (\( \text{BaCrO}_4 \)) and potassium hydroxide (\( \text{KOH} \)).
- The precipitate formed is yellow.

**Conclusion**: \( \text{BaCrO}_4 \) yields a yellow precipitate.

### Final Count
From the analysis:
- \( \text{PbCrO}_4 \) yields a yellow precipitate.
- \( \text{BaCrO}_4 \) yields a yellow precipitate.
- \( \text{Ag}_2\text{CrO}_4 \) and \( \text{Hg}_2\text{CrO}_4 \) do not yield yellow precipitates.

Thus, the number of compounds that yield a yellow color precipitate is **2**.

### Summary
The compounds that yield a yellow precipitate are:
1. \( \text{PbCrO}_4 \)
2. \( \text{BaCrO}_4 \)

**Final Answer**: 2

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