An adiabatic process is that process in which :
a.energy is transferred as heat
b.no energy is transferred as heat
c.`DeltaU = w`
d.the temp. of gas increases in a reversible compression

Options

A. energy is transferred as heat
B. no energy is transferred as heat
C. `DeltaU = w`
D. the temp. of gas increases in a reversible compression

Explanation

To solve the question regarding the characteristics of an adiabatic process, we will analyze each option step by step.

### Step-by-Step Solution:

1. **Understanding Adiabatic Process**:
- An adiabatic process is defined as a thermodynamic process in which there is no heat transfer into or out of the system. This means that any change in the internal energy of the system is due solely to work done on or by the system.

2. **Evaluating Option A**:
- **Option A: Energy is transferred as heat**.
- This statement is incorrect because, by definition, an adiabatic process does not involve heat transfer. Therefore, option A is false.

3. **Evaluating Option B**:
- **Option B: No energy is transferred as heat**.
- This statement is correct as it aligns with the definition of an adiabatic process. There is no heat transfer (ΔQ = 0) in this type of process.

4. **Evaluating Option C**:
- **Option C: ΔU = W**.
- According to the first law of thermodynamics, ΔU = ΔQ + W. Since ΔQ = 0 in an adiabatic process, it simplifies to ΔU = W. This statement is also correct.

5. **Evaluating Option D**:
- **Option D: The temperature of gas increases in a reversible compression**.
- In a reversible adiabatic compression, the volume of the gas decreases, which typically leads to an increase in temperature (due to the work done on the gas). However, the statement is misleading because it does not specify that it is a reversible process. In general, during adiabatic compression, the temperature does increase, but the phrasing could imply that it is always true without context. Therefore, this statement is somewhat ambiguous but can be considered incorrect in the context of the question.

### Conclusion:
From the analysis:
- **Correct options**: B and C
- **Incorrect options**: A and D

### Final Answer:
The correct answer is: **B and C**.