Which of the following molecule is theoretically not possible ?

Options

A. `OF_(4)`
B. `O_(2)F_(2)`
C. `OF_(2)`
D. `SF_(4)`

Explanation

To determine which of the given molecules is theoretically not possible, we need to analyze the valency of oxygen and sulfur in the context of the molecules provided: OF4, O2F2, OF2, and SF4.

### Step-by-Step Solution

1. **Understanding Valency**:
- The valency of an element refers to its ability to bond with other atoms. For oxygen, the maximum valency is 3 because it can form a maximum of three covalent bonds due to the absence of d-orbitals.

2. **Analyzing OF4**:
- In OF4, oxygen is bonded to four fluorine atoms. This implies that the valency of oxygen would need to be 4. Since the maximum valency of oxygen is 3, this molecule is theoretically not possible.

3. **Analyzing O2F2**:
- O2F2 consists of two oxygen atoms and two fluorine atoms. Each oxygen can form a bond with one fluorine atom, satisfying the valency of both oxygen (2) and fluorine (1). Thus, O2F2 is theoretically possible.

4. **Analyzing OF2**:
- In OF2, oxygen is bonded to two fluorine atoms. The valency of oxygen is satisfied (2), and the valency of fluorine (1) is also satisfied. Therefore, OF2 is theoretically possible.

5. **Analyzing SF4**:
- In SF4, sulfur can have a valency of 2, 4, or 6. Here, sulfur is bonded to four fluorine atoms, which satisfies its valency of 4. Thus, SF4 is theoretically possible.

6. **Conclusion**:
- After analyzing all the molecules, we find that OF4 is the only molecule that is theoretically not possible due to the valency limitations of oxygen.

### Final Answer:
The molecule that is theoretically not possible is **OF4**.