Which does not react with chlorine in dark

Options

A. `C_2H_4`
B. `C_2H_2`
C. `CH_4`
D. `CH_3CHO`

Answer

To determine which compound does not react with chlorine in the dark, we need to analyze the behavior of different types of hydrocarbons when exposed to chlorine.

### Step-by-Step Solution:

1. **Understanding Chlorine Reactions**: Chlorine can react with hydrocarbons in two primary ways:
- **Electrophilic Addition**: This occurs in the presence of light (UV light) and typically involves alkenes and alkynes.
- **Free Radical Substitution**: This occurs in the dark or in the presence of heat and usually involves alkanes.

2. **Types of Hydrocarbons**:
- **Alkanes (Paraffins)**: Generally, alkanes are less reactive and do not react with chlorine in the dark unless heat is applied. They require light or heat to initiate a free radical substitution reaction.
- **Alkenes (Olefins)**: Alkenes are more reactive and can react with chlorine in the presence of light through electrophilic addition.
- **Alkynes**: Similar to alkenes, alkynes can also react with chlorine in the presence of light.

3. **Identifying the Non-Reactive Hydrocarbon**:
- Since alkanes are known for their low reactivity and do not react with chlorine in the dark, we can conclude that the hydrocarbon that does not react with chlorine in the dark is an alkane.

4. **Conclusion**: The correct answer to the question "Which does not react with chlorine in the dark?" is **alkanes**.