In an isothermal irreversible expansion of an ideal gas as per IUPAC sign convention :

Options

A. `DeltaU = 0`
B. `DeltaH = 0`
C. `w=-nRTln.(P_(1))/(P_(2))`
D. `w=-q`

Explanation

To solve the question regarding the isothermal irreversible expansion of an ideal gas as per IUPAC sign convention, we will analyze the statements related to work and heat transfer.

### Step-by-Step Solution:

1. **Understanding Isothermal Expansion**:
- In an isothermal process, the temperature of the system remains constant. For an ideal gas, this means that any change in volume will result in a corresponding change in pressure.

2. **Work Done by the System**:
- During the expansion of the gas, the system (gas) does work on the surroundings. According to the IUPAC sign convention, work done by the system is considered negative. Therefore, if the gas expands and pushes against the external pressure, the work done (W) is negative.

3. **Work Done on the System**:
- Conversely, if work is done on the system (for example, if the gas is compressed), it would be considered positive. However, in the case of expansion, this situation does not apply.

4. **Heat Transfer**:
- In an isothermal process, the gas absorbs heat (Q) from the surroundings to maintain its temperature. According to the IUPAC sign convention, heat absorbed by the system is considered positive. Therefore, during the expansion, heat absorbed by the gas is positive.

5. **Heat Released to the Surroundings**:
- If the system were to release heat to the surroundings, that would be considered negative. However, in the case of isothermal expansion, the gas absorbs heat from the surroundings, so this situation does not apply.

### Summary of Statements:
- Work done by the system on the surroundings: **Negative**
- Work done by the surroundings on the system: **Positive**
- Heat absorbed by the system: **Positive**
- Heat released by the system to the surroundings: **Negative**

### Conclusion:
Based on the analysis:
- The correct statements according to the IUPAC sign convention are:
- Work done by the system on the surroundings is negative.
- Heat absorbed by the system is positive.