Which of the following is not isostructural with `SiCI_(4)` ?

Options

A. `SO_(4)^(2-)`
B. `PO_(4)^(3-)`
C. `NH_(4)^(+)`
D. `SCl_(4)`

Answer

To determine which of the following compounds is not isostructural with SiCl₄, we need to analyze the structures of each compound listed in the options and compare them with the structure of SiCl₄.

### Step-by-Step Solution:

1. **Identify the Structure of SiCl₄:**
- SiCl₄ (Silicon Tetrachloride) has a tetrahedral geometry.
- The central silicon atom is bonded to four chlorine atoms, and there are no lone pairs on the silicon atom.

2. **Analyze the First Option: SO₄²⁻ (Sulfate Ion):**
- The sulfate ion has a central sulfur atom bonded to four oxygen atoms.
- The geometry of SO₄²⁻ is also tetrahedral, similar to SiCl₄.

3. **Analyze the Second Option: PO₄³⁻ (Phosphate Ion):**
- The phosphate ion has a central phosphorus atom bonded to four oxygen atoms.
- The geometry of PO₄³⁻ is also tetrahedral, similar to SiCl₄.

4. **Analyze the Third Option: NH₄⁺ (Ammonium Ion):**
- The ammonium ion has a central nitrogen atom bonded to four hydrogen atoms.
- The geometry of NH₄⁺ is also tetrahedral, similar to SiCl₄.

5. **Analyze the Fourth Option: SCl₄ (Sulfur Tetrachloride):**
- The sulfur atom in SCl₄ is bonded to four chlorine atoms, but sulfur has six valence electrons.
- This means that two of the electrons are left as a lone pair on the sulfur atom.
- The presence of a lone pair results in a seesaw shape (trigonal bipyramidal geometry) rather than a tetrahedral shape.

6. **Conclusion:**
- Among the options, SO₄²⁻, PO₄³⁻, and NH₄⁺ all have tetrahedral geometries and are isostructural with SiCl₄.
- SCl₄, however, has a different geometry due to the lone pair on sulfur and is not isostructural with SiCl₄.

### Final Answer:
The compound that is not isostructural with SiCl₄ is **SCl₄**.