Question

In which of the following pairs, both the species are not isostructural ?

• A. ${ NH3, PH3}$
• B. ${ XeF4, XeO4}$
• C. ${ SiCl4, PCl_4^+}$
• D. Dimond, silicon carbide

Answer 1

The Correct Option is B

To determine which pair of species are not isostructural, we must define and examine the term "isostructural". Two species are considered isostructural if they have the same geometrical arrangement or shape.

1. ${ NH_3, PH_3 }$:

   Both ammonia (NH_3) and phosphine (PH_3) are trigonal pyramidal in shape. This is because both have a central nitrogen or phosphorus atom bonded to three hydrogen atoms with a lone pair, following VSEPR theory.

2. ${ XeF_4, XeO_4}$:

   Xenon tetrafluoride (XeF_4) is square planar, whereas xenon tetroxide (XeO_4) is tetrahedral. This difference in geometry is due to the distinct electron pair arrangements in each compound. Therefore, these are not isostructural.

3. ${ SiCl_4, PCl_4^+}$:

   Both silicon tetrachloride (SiCl_4) and the phosphonium ion (PCl_4^+) are tetrahedral. Thus, they are isostructural.

4. Diamond, silicon carbide:

   Diamond consists of carbon atoms in a tetrahedral structure. Silicon carbide, commonly found in a similar tetrahedral crystalline structure (e.g., cubic), makes them isostructural.

Conclusively, the pair ${ XeF_4, XeO_4}$ consists of species that are not isostructural. Hence, the correct answer is ${ XeF_4, XeO_4}$.