Which of the following reactions has positive ΔS° value?

$2C (s) + O_2(g) → 2CO (g)$

The correct answer is Option (2) → $2C (s) + O_2(g) → 2CO (g)$

To determine which reaction has a positive \( \Delta S^\circ \) (change in entropy), we need to consider the changes in the number of gas molecules and the states of matter involved in each reaction. A positive \( \Delta S^\circ \) typically occurs when the number of gaseous products increases or when solid reactants are converted into gaseous products.

Reactions Analysis:

1. \( 6 \text{FeO}(s) + \text{O}_2(g) \rightarrow 2 \text{Fe}_3\text{O}_4(s) \):

Reactants: 1 gas molecule (\( \text{O}_2 \))

Products: 0 gas molecules

Change: Decrease in entropy (negative \( \Delta S^\circ \))

2. \( 2 \text{C}(s) + \text{O}_2(g) \rightarrow 2 \text{CO}(g) \):

Reactants: 1 gas molecule (\( \text{O}_2 \))

Products: 2 gas molecules (\( 2 \text{CO} \))

Change: Increase in entropy (positive \( \Delta S^\circ \))

3. \( 4 \text{Al}(s) + 3 \text{O}_2(g) \rightarrow 2 \text{Al}_2\text{O}_3(s) \):

Reactants: 3 gas molecules (\( 3 \text{O}_2 \))

Products: 0 gas molecules

Change: Decrease in entropy (negative \( \Delta S^\circ \))

4. \( 2 \text{CO}(g) + \text{O}_2(g) \rightarrow 2 \text{CO}_2(g) \):

Reactants: 3 gas molecules (\( 2 \text{CO} + \text{O}_2 \))

Products: 2 gas molecules (\( 2 \text{CO}_2 \))

Change: Decrease in entropy (negative \( \Delta S^\circ \))

Conclusion
The reaction that has a positive \( \Delta S^\circ \) value is:

\( 2 \text{C}(s) + \text{O}_2(g) \rightarrow 2 \text{CO}(g) \).

The correct answer is Option (2) → $2C (s) + O_2(g) → 2CO (g)$