At least two different numbers of electron groups can result in a linear molecular geometry. Which numbers of electron groups can lead to a linear molecule?

• A. $2$ and $5$
• B. $3$ and $5$
• C. $2$ and $4$
• D. $3$ and $4$

Answer: (A)

Verified step by step guidance

1. Recall that the molecular geometry depends on the number of electron groups (bonding and lone pairs) around the central atom and their arrangement to minimize repulsion, according to VSEPR theory.
2. Identify the electron group geometries that can produce a linear molecular shape. For 2 electron groups, the geometry is linear by default, with a bond angle of 180°.
3. Consider the case of 3 electron groups. The electron geometry is trigonal planar, but if there are 2 bonding groups and 1 lone pair, the molecular shape is bent, not linear.
4. For 4 electron groups, the electron geometry is tetrahedral. None of the molecular shapes derived from this geometry are linear because bond angles are approximately 109.5°.
5. For 5 electron groups, the electron geometry is trigonal bipyramidal. If there are 2 bonding groups and 3 lone pairs arranged in the equatorial positions, the molecular shape can be linear with bond angles of 180°.