Which of the following can produce a colour change from yellowish brown to light green in acidified aqueous solution of iron (III) chloride?

Options

A. `H_(2)` gas
B. `O_(2)`
C. Addition of zinc and HCI
D. Simple addition of HCI

Answer

To solve the question of which substance can produce a color change from yellowish brown to light green in an acidified aqueous solution of iron (III) chloride (FeCl3), we can follow these steps:

### Step 1: Understand the Initial Color and State
- Iron (III) chloride (FeCl3) is yellowish brown in color due to the presence of iron in the +3 oxidation state (Fe³⁺).

**Hint:** Remember that the color of a compound can indicate its oxidation state.

### Step 2: Identify the Desired Color Change
- The question states that we want to achieve a color change to light green. This color is typically associated with iron in the +2 oxidation state (Fe²⁺), which corresponds to iron (II) chloride (FeCl2).

**Hint:** Identify the oxidation states of iron associated with the colors.

### Step 3: Determine the Reaction Required
- To convert Fe³⁺ (yellowish brown) to Fe²⁺ (light green), a reduction reaction must occur. This means that we need to reduce Fe³⁺ to Fe²⁺.

**Hint:** Reduction involves gaining electrons or a decrease in oxidation state.

### Step 4: Identify Possible Reducing Agents
- A common reducing agent that can provide nascent hydrogen is zinc (Zn) when it reacts with hydrochloric acid (HCl). The reaction is as follows:
\[ \text{Zn} + 2\text{HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2 \]
- The nascent hydrogen produced can reduce Fe³⁺ to Fe²⁺.

**Hint:** Look for reactions that produce nascent hydrogen or other reducing agents.

### Step 5: Conclusion
- Among the options provided, the combination of zinc and hydrochloric acid (Zn + HCl) is the correct choice, as it produces nascent hydrogen, which can reduce Fe³⁺ to Fe²⁺, resulting in the desired color change from yellowish brown to light green.

**Final Answer:** The correct option is the combination of Zinc and HCl.