Hot water in a thermos flask is an example for

Options

A. Isolated system
B. Open system
C. Closed system
D. Adiabatic system

Answer

To solve the question, "Hot water in a thermos flask is an example of," we need to analyze the characteristics of a thermos flask and the system it represents.

### Step-by-Step Solution:

1. **Understanding the Thermos Flask**:
- A thermos flask is designed to keep liquids hot or cold by minimizing heat transfer with the environment. It typically has double walls with a vacuum in between, which prevents heat conduction and convection.

2. **Identifying Heat Transfer**:
- In the case of hot water in a thermos, the heat from the water does not escape to the surroundings, and external heat does not enter the flask. This indicates that there is no heat transfer (dq = 0).

3. **Identifying Mass Transfer**:
- Similarly, since the thermos is sealed, there is no mass transfer occurring. The amount of water inside the thermos remains constant (dm = 0).

4. **Defining the System**:
- A system where neither heat nor mass can be exchanged with the surroundings is classified as an isolated system.

5. **Conclusion**:
- Therefore, hot water in a thermos flask is an example of an isolated system.

### Final Answer:
Hot water in a thermos flask is an example of an **isolated system**.

---