Choose the correct optios.

Options

A. Good absorbers of a particular wavelength are good emitters of same wavelength. This statement was given by Kirchhoff.
B. At low temperature of a body the rate of cooling is directly proportional to temperature of the body. This statement was given by the Newton
C. Emissive power of a perfectly black body is 1
D. Absorptive power of a perfectly black body is 1

Explanation

To solve the question, we need to analyze the statements provided and determine which options are correct based on principles of physics, particularly those related to thermodynamics and heat transfer.

### Step-by-Step Solution:

1. **Understanding Kirchhoff's Law**:
- Kirchhoff's law states that for a body in thermal equilibrium, the ratio of the emissive power to the absorptive power is constant and depends only on the temperature and wavelength. This means that good absorbers are also good emitters at a given wavelength.
- **Hint**: Remember that Kirchhoff's law relates absorption and emission properties of materials.

2. **Newton's Law of Cooling**:
- Newton's law of cooling states that the rate of heat loss of a body is proportional to the difference in temperature between the body and its surroundings, provided this temperature difference is small. This means that as the temperature difference decreases, the rate of cooling also decreases.
- **Hint**: Consider how temperature differences affect the rate of heat transfer.

3. **Black Body Radiation**:
- A black body is defined as an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. It is also a perfect emitter of radiation.
- **Hint**: Recall the characteristics of black bodies in thermodynamics.

4. **Evaluating the Statements**:
- The first statement about Kirchhoff's law is true.
- The second statement regarding Newton's law of cooling is also true, but only under the condition of small temperature differences.
- The statement about black bodies is true as they are perfect absorbers and emitters.
- The statement about the rate of cooling being proportional to the temperature difference is true under specific conditions (small temperature differences).

5. **Determining the Correct Options**:
- Based on the analysis, the correct options would be those that align with the established laws of thermodynamics and heat transfer.
- If the options provided in the question include statements that are consistent with Kirchhoff's law, Newton's law of cooling, and the properties of black bodies, those would be the correct choices.

### Conclusion:
The correct options based on the analysis would be those that reflect the principles outlined above, particularly options related to Kirchhoff's law and the properties of black bodies.

### Final Answer:
The correct options are **C and D** based on the principles discussed.