Substitution reactions of alkanes are carried out at

Options

A. High temperature
B. Low temperature
C. Moderate temperature
D. Very low temperature

Answer

To determine the conditions under which substitution reactions of alkanes occur, we can analyze the nature of these reactions and the factors that influence them.

### Step-by-Step Solution:

1. **Understanding Substitution Reactions**:
- Substitution reactions involve the replacement of one atom or group in a molecule with another atom or group. In alkanes, this typically involves the substitution of hydrogen atoms with halogens (like chlorine or bromine).

2. **Characteristics of Alkanes**:
- Alkanes are saturated hydrocarbons (e.g., methane, ethane) that are generally nonpolar due to the small electronegativity difference between carbon and hydrogen (less than 0.5). This nonpolarity affects how they react with other substances.

3. **Conditions for Substitution Reactions**:
- Substitution reactions of alkanes require specific conditions to proceed effectively. These conditions include the presence of a halogen and a source of energy, such as heat or light.

4. **Role of Temperature**:
- High temperatures are often necessary to initiate and sustain these reactions. This is because the energy provided at high temperatures helps to break the C-H bonds in alkanes and allows for the substitution to occur.

5. **Examples of Substitution Reactions**:
- For instance, when methane (CH₄) reacts with chlorine (Cl₂) in the presence of UV light (Hν), it forms chloromethane (CH₃Cl) and hydrochloric acid (HCl). This reaction is facilitated by the high temperature and the energy from light.

6. **Conclusion**:
- Based on the analysis, substitution reactions of alkanes are predominantly carried out at **high temperatures**. Low, moderate, or very low temperatures do not provide sufficient energy for the reaction to occur.

### Final Answer:
The substitution reactions of alkanes are carried out at **high temperature**.

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