Answer:
Because they have the same arrangement of atoms in space. Both have a straight line or a flat triangular arrangement of atoms, respectively, with bond angles of 180° and 120° respectively. In 2-dimensional drawings, it is not possible to see the differences in the three-dimensional arrangement of atoms, so both linear and trigonal planar molecules appear as a straight line or a flat triangle. However, in three dimensions, it is possible to see the differences in the arrangement of the bonds and the orientation of the molecule in space, allowing us to distinguish between linear and trigonal planar molecules.
Step-by-step explanation:
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