Chemistry · EQUILIBRIUM

In the equilibrium \( \text{Fe}^{3+}(\text{aq}) + \text{SCN}^-(\text{aq}) \rightleftharpoons [\text{Fe}(\text{SCN})]^{2+}(\text{aq}) \) (deep red), what happens to the red colour intensity upon the addition of oxalic acid \( (\text{H}_2\text{C}_2\text{O}_4) \) and why?

1. Red colour intensity increases because it reacts with \( \text{SCN}^- \) to form \( [\text{Fe}(\text{SCN})_2]^+ \)
2. Red colour intensity increases because it acts as a reducing agent converting \( \text{Fe}^{3+} \) to \( \text{Fe}^{2+} \)
3. Red colour intensity remains unchanged because oxalic acid does not react with either ion
4. Red colour intensity decreases because it forms a stable complex \( [\text{Fe}(\text{C}_2\text{O}_4)_3]^{3-} \), removing free \( \text{Fe}^{3+} \) ions