The following reaction is at equilibrium ,
`underset("Yellow")(Fe_((aq))^(3+))+ underset("Colourless")(SCN_((aq)))rArrunderset("Deep red")([Fe(SNC)]_((aq))^(2+))`
`K_(c)=([Fe(SCN)])/([Fe^(3+)][SCN])`
In the above reaction , colour intensity of red colour can be increased by :-

Options

A. (a)addition of KSCN
B. (b)addition of oxalic acid which reacts with `Fe^(3+)` ions
C. (c)addition of `Hg^(2+)` ions which react with `SCN^(-)` ions
D. (d)red colour intensity cannot be changed

Answer

To solve the problem, we need to analyze the given equilibrium reaction and apply Le Chatelier's principle to determine how to increase the intensity of the red color produced by the reaction.

### Step-by-Step Solution:

1. **Identify the Reaction and Equilibrium Expression**:
The reaction is:
\[ \text{Fe}^{3+}_{(aq)} + \text{SCN}^-_{(aq)} \rightleftharpoons \text{Fe(SCN)}^{2+}_{(aq)} \]
The equilibrium constant expression \( K_c \) is given by:
\[ K_c = \frac{[\text{Fe(SCN)}^{2+}]}{[\text{Fe}^{3+}][\text{SCN}^-]} \]

2. **Understand the Color Change**:
The product \(\text{Fe(SCN)}^{2+}\) is deep red in color. To increase the intensity of this red color, we need to increase the concentration of the product \([\text{Fe(SCN)}^{2+}]\).

3. **Apply Le Chatelier's Principle**:
According to Le Chatelier's principle, if we change the concentration of either reactant or product, the equilibrium will shift to counteract that change. To increase the concentration of the product, we can either:
- Increase the concentration of a reactant (which shifts the equilibrium to the right).
- Remove a product (which also shifts the equilibrium to the right).

4. **Evaluate the Options**:
- **Addition of KSCN**: This will increase the concentration of \(\text{SCN}^-\), one of the reactants. According to Le Chatelier's principle, the equilibrium will shift to the right, increasing the concentration of \(\text{Fe(SCN)}^{2+}\) and thus the red color intensity.
- **Addition of Oxalic Acid**: This reacts with \(\text{Fe}^{3+}\), decreasing its concentration. This will shift the equilibrium to the left, reducing the red color intensity.
- **Addition of Hg\(^{2+}\)**: This reacts with \(\text{SCN}^-\), decreasing its concentration. This will also shift the equilibrium to the left, reducing the red color intensity.
- **Red color intensity cannot be changed**: This statement is incorrect as we can change the intensity by adjusting reactant concentrations.

5. **Conclusion**:
The correct answer is the addition of KSCN, which will increase the concentration of \(\text{SCN}^-\) and shift the equilibrium to the right, enhancing the red color intensity.

### Final Answer:
The color intensity of the red color can be increased by the addition of KSCN.

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