Question

Which of the following are isostructural pairs? A. $SO _{4}^{2-}$ and $CrO _{4}^{2-}$ B. $SiCl _{4}$ and $TiCl _{4}$ C. $NH _{3}$ and $NO _{3}^{-}$ D. $BCl _{3}$ and $BrCl _{3}$ $BCl _{3}$ and $BrCl _{3}$

• A. $C$ and $D$ only
• B. $A$ and $B$ only
• C. $A$ and $C$ only
• D. $B$ and $C$ only

Answer 1

The Correct Option is B

To determine the isostructural pairs, we need to understand what is meant by "isostructural." Isostructural compounds have the same shape and bond angles but may differ in the elements involved. Let's evaluate each pair:

1. $SO_{4}^{2-}$ and $CrO_{4}^{2-}$:
   • Both $SO_{4}^{2-}$ (sulfate ion) and $CrO_{4}^{2-}$ (chromate ion) are tetrahedral in shape.
   • They each have a central atom surrounded by four oxygen atoms and possess the same overall geometry.
   • Thus, they are isostructural.
2. $SiCl_{4}$ and $TiCl_{4}$:
   • Both $SiCl_{4}$ (silicon tetrachloride) and $TiCl_{4}$ (titanium tetrachloride) have a tetrahedral geometry.
   • The central Si and Ti atoms are both surrounded by four chlorine atoms.
   • Therefore, they are isostructural.
3. $NH_{3}$ and $NO_{3}^{-}$:
   • $NH_{3}$ (ammonia) has a trigonal pyramidal shape.
   • $NO_{3}^{-}$ (nitrate ion) has a trigonal planar shape.
   • Since their geometrical structures differ, they are not isostructural.
4. $BCl_{3}$ and $BrCl_{3}$:
   • $BCl_{3}$ (boron trichloride) is trigonal planar.
   • $BrCl_{3}$ actually exists in a $\text{T}$-shape due to the presence of lone pairs on Br, which is different compared to trigonal planar.
   • Thus, these two are not isostructural.

Based on the above analysis, the correct isostructural pairs are $A$ and $B$ only.