What is meant by a linear molecule?

A linear molecule is characterized by its atoms being arranged in a straight line. This structural arrangement allows the bond angles between all atoms to be 180 degrees, which is a key feature of linear geometry. Common examples of linear molecules include diatomic molecules such as hydrogen (H2) or carbon dioxide (CO2), where the atoms are directly connected with no other atoms forcing them into a different configuration.

In contrast to the other options, a circular arrangement refers to a closed shape, while bond angles of 120 degrees typically belong to trigonal planar geometries and do not apply to linear structures. Additionally, a molecule consisting only of single atoms does not qualify as a molecule in the traditional sense; instead, it represents individual atoms rather than a distinct molecular structure. Thus, the defining aspect of a linear molecule is its straight-line arrangement of atoms.