Question

Two molecules have the same molecular geometry but different electron domain geometries. Which combination of atoms and lone pairs around the central atom could describe these molecules?
2 atoms and 2 lone pairs; 3 atoms and 0 lone pairs
1 atom and 3 lone pairs; 2 atoms and 1 lone pair
3 atoms and 1 lone pair; 3 atoms and 0 lone pairs
2 atoms and 2 lone pairs; 2 atoms and 1 lone pair

Answer 1

Answer : The correct option is, 2 atoms and 2 lone pairs; 2 atoms and 1 lone pair

Explanation :

In type $AB_3$, when bond pair of electrons is 2 and lone pair of electrons is 1 then the electron domain geometry is Trigonal planar and molecular geometry is Bent.

In type $AB_4$, when bond pair of electrons is 2 and lone pair of electrons is 2 then the electron domain geometry is Tetrahedral and molecular geometry is Bent.

Hence, a molecule having 2 atoms and 2 lone pair have the same molecular geometry as that of the molecule having 2 atoms and 1 lone pair.

The table is shown below.

Answer 2

The correct answer is:
2 atoms and 2 lone pairs; 2 atoms and 1 lone pair.
Both AX₂E₂ and AX₂E have different electron domain geometry; AX₂E₂ is tetrahedral and AX₂E is trigonal planar but both of them has the same molecular geometry Bent