Which of the following statements is correct?

Options

A. The presence of reacting species in a covered beaker is an example of open system.
B. There is an exchange of energy as well as matter between the system and the surroundings in a closed system.
C. The presnce of reactants in a closed vessel made up of copper is an example of a closed system.
D. The presence of reactants in a thermos flask or any other closed insulated vessel is an example of a closed system.

Explanation

To solve the question "Which of the following statements is correct?" we will analyze each statement one by one and determine its validity based on the principles of thermodynamics.

### Step-by-Step Solution:

1. **Statement Analysis**:
- **Statement 1**: "The presence of reacting species in a covered beaker is an example of an open system."
- **Analysis**: A covered beaker does not allow the exchange of matter with the surroundings, thus it is not an open system. This statement is **incorrect**.

- **Statement 2**: "In a closed system, the matter can change."
- **Analysis**: In a closed system, matter cannot be exchanged with the surroundings, although energy can be exchanged. This statement is **incorrect**.

- **Statement 3**: "The presence of reactants in a closed vessel made up of copper is an example of a closed system."
- **Analysis**: A closed vessel allows for the exchange of energy but not matter. Therefore, this statement is **correct**.

- **Statement 4**: "The presence of reactants in a thermos flask or any other closed insulated vessel is an example of a closed system."
- **Analysis**: While a thermos flask is designed to minimize heat transfer (adiabatic), it is still a closed system in terms of matter. However, if it is perfectly insulated, it may not allow any heat exchange, making it an adiabatic system. This statement can be misleading and is generally considered **incorrect** in the context of thermodynamics.

2. **Conclusion**:
- After analyzing all the statements, the only correct statement is **Statement 3**: "The presence of reactants in a closed vessel made up of copper is an example of a closed system."

### Final Answer:
The correct statement is **Statement 3**.

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