Which among the following compound cannot be prepared by direct union of elements ?

Options

A. `SF_(6)`
B. `Se_(2)Br_(2)`
C. `S_(2)Cl_(2)`
D. `SF_(4)`

Answer

To determine which compound cannot be prepared by the direct union of elements, we need to analyze each option provided. The term "direct union of elements" refers to the formation of a compound solely from its constituent elements without the involvement of other compounds or complex reactions.

### Step-by-Step Solution:

1. **Identify the Compounds:**
Let's assume the options provided are:
a) SF6
b) ScBr2
c) S2Cl2
d) SF4

2. **Analyze Each Compound:**
- **For SF6 (Sulfur Hexafluoride):**
- The reaction can be represented as:
\[ S + 3F2 \rightarrow SF6 \]
- This is a direct combination of sulfur and fluorine. Thus, SF6 can be prepared by direct union.

- **For ScBr2 (Scandium Bromide):**
- The reaction can be represented as:
\[ 2Sc + Br2 \rightarrow ScBr2 \]
- This is also a direct combination of scandium and bromine. Therefore, ScBr2 can be prepared by direct union.

- **For S2Cl2 (Disulfur Dichloride):**
- The reaction can be represented as:
\[ S2 + Cl2 \rightarrow S2Cl2 \]
- This is a direct combination of sulfur and chlorine. Thus, S2Cl2 can also be prepared by direct union.

- **For SF4 (Sulfur Tetrafluoride):**
- The reaction can be represented as:
\[ S + 2F2 \rightarrow SF4 \]
- However, this reaction typically requires specific conditions (like temperature) and may involve other compounds or intermediates, indicating that it is not a straightforward direct union of elements.

3. **Conclusion:**
- Based on the analysis, the compound that cannot be prepared by the direct union of elements is **SF4**.

### Final Answer:
The compound that cannot be prepared by direct union of elements is **SF4**.