\begin{tabular}{|l|l|l|}
\hline hydrogen carbonate (bicarbonate) & [tex]$HCO_3^{-}$[/tex] & hydroxide \\
\hline chlorite & [tex]$ClO_2^{-}$[/tex] & peroxide \\
\hline & & \\
\hline
\end{tabular}

Select the correct answer.

What are the oxidizing agent and the reducing agent in this chemical equation?

[tex]\[ 3 FeS + 8 HNO_3 \rightarrow 3 FeSO_4 + 8 NO + 4 H_2O \][/tex]

A. FeS is the oxidizing agent, and [tex]$HNO_3$[/tex] is the reducing agent.

B. [tex]$HNO_3$[/tex] is the oxidizing agent, and [tex]$NO$[/tex] is the reducing agent.

C. FeS is the reducing agent, and [tex]$HNO_3$[/tex] is the oxidizing agent.

D. [tex]$HNO_3$[/tex] is the reducing agent, and [tex]$NO$[/tex] is the oxidizing agent.



Answer :

To determine the oxidizing and reducing agents in the chemical equation [tex]\(3 \text{FeS} + 8 \text{HNO}_3 \rightarrow 3 \text{FeSO}_4 + 8 \text{NO} + 4 \text{H}_2\text{O}\)[/tex], we need to analyze the changes in oxidation states of the elements involved.

1. Identify the initial oxidation states:
- Fe in FeS: The oxidation state of Fe in FeS is +2 (since sulfur is usually -2 in compounds).
- S in FeS: The oxidation state of sulfur in FeS is -2.
- N in HNO[tex]\(_3\)[/tex]: Nitrogen in HNO[tex]\(_3\)[/tex] has an oxidation state of +5 (since oxygen is -2 and hydrogen is +1).

2. Identify the final oxidation states:
- Fe in FeSO[tex]\(_4\)[/tex]: Iron (Fe) in FeSO[tex]\(_4\)[/tex] is +2.
- S in FeSO[tex]\(_4\)[/tex]: Sulfur (S) in FeSO[tex]\(_4\)[/tex] is +6 (since sulfate, SO[tex]\(_4^{2-}\)[/tex], has a -2 charge and each oxygen is -2).
- N in NO: Nitrogen in NO has an oxidation state of +2.

3. Determine the changes in oxidation states:
- Fe remains at +2, indicating no change for Fe.
- S goes from -2 in FeS to +6 in FeSO[tex]\(_4\)[/tex]. This is an increase of 8, meaning sulfur is oxidized.
- N goes from +5 in HNO[tex]\(_3\)[/tex] to +2 in NO. This is a decrease of 3, meaning nitrogen is reduced.

4. Determine the agents:
- The substance being oxidized (in losing electrons) is FeS. Hence, FeS is the reducing agent because it provides electrons to another species.
- The substance gaining electrons/reducing (increasing in oxidation state) is HNO[tex]\(_3\)[/tex], which is therefore the oxidizing agent as it accepts electrons from another species.

Thus, the correct answer is:
C. FeS is the reducing agent, and [tex]\( \text{HNO}_3 \)[/tex] is the oxidizing agent.

So, the true answer is option C.