The colour chage observed when excess ethyne is passed through the solution of bromine water is

Options

A. Colourless to reddish brown
B. Colourless to green
C. reddish brown to colourless
D. Pink to colourless

Answer

To solve the question regarding the color change observed when excess ethyne is passed through bromine water, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Reactants**:
- The reactant in this case is ethyne (C2H2), which is an alkyne.

2. **Understand the Reaction**:
- When ethyne is passed through bromine water, it undergoes an addition reaction. Ethyne can react with bromine (Br2) to form a dibrominated product.

3. **Reaction Mechanism**:
- Ethyne reacts with bromine to form 1,2-dibromoethane. The reaction can be represented as:
\[ C_2H_2 + Br_2 \rightarrow C_2H_2Br_2 \]
- Here, each carbon atom in ethyne adds a bromine atom, resulting in 1,2-dibromoethane.

4. **Color Change Observation**:
- Bromine water is initially reddish-brown due to the presence of bromine (Br2).
- As ethyne reacts with bromine, the reddish-brown color of the bromine water disappears, resulting in a colorless solution. This is because bromine is consumed in the reaction.

5. **Conclusion**:
- The color change observed when excess ethyne is passed through bromine water is from reddish-brown to colorless.

### Final Answer:
The color change observed is from reddish-brown to colorless.

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