Which of the following rection is/are correct?

Options

A. `C_xH_y+(x+(y)/(2))O_2rarrxCO_2+(y)/(2)H_2O`
B. `4Fe^(3+)+[Fe(CN)_6]^(4-)rarrFe_3[Fe(CN)_6]_4`
C. `5CO+I_2O_5rarrI_2+5CO_2`
D. `Pb^(2+)+S^(2-)rarrPbS`

Explanation

To determine which of the given reactions are correct, we will analyze each reaction step by step.

### Step 1: Analyze the First Reaction
The first reaction is:
\[ \text{C}_x\text{H}_y + \left(x + \frac{y}{2}\right) \text{O}_2 \rightarrow x \text{CO}_2 + \frac{y}{2} \text{H}_2\text{O} \]

**Analysis:**
- This reaction represents the combustion of a hydrocarbon.
- A hydrocarbon (CxHy) reacts with oxygen (O2) to produce carbon dioxide (CO2) and water (H2O).
- The stoichiometry is correct: one mole of hydrocarbon reacts with the appropriate amount of oxygen to yield the correct amounts of CO2 and H2O.

**Conclusion:** The first reaction is correct.

### Step 2: Analyze the Second Reaction
The second reaction is:
\[ 4 \text{Fe}^{3+} + \text{Fe(CN)}_6^{4-} \rightarrow \text{Fe}_4\text{Fe(CN)}_6 \]

**Analysis:**
- This reaction involves ferric ions (Fe3+) and ferrocyanide ions (Fe(CN)6^4-).
- The expected product is Prussian blue, which is represented as \(\text{Fe}_3[\text{Fe(CN)}_6]\).
- The stoichiometry and the product are incorrect as written in the reaction.

**Conclusion:** The second reaction is incorrect.

### Step 3: Analyze the Third Reaction
The third reaction is:
\[ 5 \text{CO} + \text{I}_2\text{O}_5 \rightarrow \text{I}_2 + 5 \text{CO}_2 \]

**Analysis:**
- This reaction shows carbon monoxide (CO) reacting with iodine pentoxide (I2O5).
- The products are iodine (I2) and carbon dioxide (CO2).
- The stoichiometry is correct, and this reaction is used for the estimation of oxygen.

**Conclusion:** The third reaction is correct.

### Step 4: Analyze the Fourth Reaction
The fourth reaction is:
\[ \text{Pb}^{2+} + \text{S}^{2-} \rightarrow \text{PbS} \]

**Analysis:**
- This reaction involves lead ions (Pb2+) reacting with sulfide ions (S2-).
- The product is lead sulfide (PbS), which is a black precipitate.
- The stoichiometry is correct.

**Conclusion:** The fourth reaction is correct.

### Final Answer
The correct reactions are:
1. First reaction
2. Third reaction
3. Fourth reaction

### Summary of Correct Reactions
- **Correct Reactions:** 1, 3, and 4.

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