Regarding the internal energy of the molecule, which of the following statement is correct?

Options

A. Its absolute value can be successfully calculated.
B. Its absolute value cannot be determined.
C. It is the sum of vibrational and rotational energies.
D. Both (1) & (3)

Answer

To determine the correct statement regarding the internal energy of a molecule, we can analyze the options provided:

### Step-by-Step Solution:

1. **Understanding Internal Energy**: Internal energy (U) is a state function that represents the total energy contained within a system. It includes various forms of energy such as kinetic energy (due to molecular motion) and potential energy (due to molecular interactions).

2. **State Function vs. Path Function**:
- A **state function** is a property that depends only on the current state of the system, not on how it reached that state. Examples include internal energy, enthalpy, and pressure.
- A **path function** depends on the specific path taken to reach a particular state. Examples include heat (q) and work (w).

3. **Absolute Values of Internal Energy**:
- The absolute value of internal energy cannot be determined because it is defined relative to a reference state. We can only measure changes in internal energy (ΔU) between two states, not its absolute value.

4. **Components of Internal Energy**:
- Internal energy is indeed the sum of various forms of energy, including translational, rotational, and vibrational energies. Thus, it is not limited to just vibrational and rotational energies.

5. **Evaluating the Statements**:
- **Statement 1**: "Absolute values can be successfully calculated." - This is incorrect because we cannot determine the absolute value of internal energy.
- **Statement 2**: "Cannot be successfully determined." - This is correct as we cannot determine the absolute value of internal energy.
- **Statement 3**: "The sum is the sum of vibrational and rotational energies." - This is partially correct, but it is incomplete because it omits translational energy.

6. **Conclusion**: The only correct statement regarding the internal energy of a molecule is that its absolute value cannot be determined.

### Final Answer:
The correct statement is: **The absolute value of internal energy cannot be determined.**