According to VSEPR theory, a molecule of the type $\text{AB}_5$ (where the central atom 'A' has 5 bond pairs and 0 lone pairs) has a trigonal bipyramidal geometry (e.g., $\text{PCl}_5$) . A square pyramidal geometry is observed in molecules of the type $\text{AB}_5\text{E}$, where the central atom has 5 bond pairs and 1 lone pair (e.g., $\text{BrF}_5$) . Therefore, the statement that every $\text{AB}_5$ molecule has a square pyramidal structure is incorrect. The other statements are true: electron-deficient species act as Lewis acids , canonical (resonance) structures are hypothetical and have no real existence , and multiple bonds (double/triple) are shorter than their corresponding single bonds .