The means of energy transfer in vacuum is:

Options

A. irradiation
B. convection
C. radiation
D. conduction

Explanation

To solve the question about the means of energy transfer in a vacuum, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Options**: The question presents different methods of energy transfer: conduction, convection, and radiation. We need to analyze each method to determine which one can occur in a vacuum.

2. **Analyze Conduction**: Conduction is the transfer of energy through direct contact between materials. It requires matter (solid, liquid, or gas) to facilitate the transfer of energy through molecular interactions. Since a vacuum lacks matter, conduction cannot occur in a vacuum.

3. **Analyze Convection**: Convection is the transfer of heat through the movement of fluids (liquids or gases). It relies on the presence of matter to carry thermal energy from one place to another. As with conduction, convection cannot occur in a vacuum due to the absence of matter.

4. **Analyze Radiation**: Radiation is the transfer of energy through electromagnetic waves. Unlike conduction and convection, radiation does not require a medium (matter) to transfer energy. It can occur in a vacuum, as electromagnetic waves (like light) can travel through empty space.

5. **Conclusion**: Since conduction and convection cannot occur in a vacuum, and radiation can, the correct answer to the question is radiation.

### Final Answer:
The means of energy transfer in vacuum is **radiation**.

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