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Which of the following is not a correct statement :-
A
The electron-deficient molecules can act as Lewis acids
B
The canonical structures have no real existence
C
Every $AB_5$ molecule does in fact have square pyramid structure
D
Multiple bonds are always shorter than corresponding single bonds
Detailed Solution
The shape of an $AB_5$ molecule depends on whether the central atom has lone pairs.
An $AB_5$ molecule with no lone pair on the central atom, such as $PCl_5$, is $sp^3d$ hybridised and has a trigonal bipyramidal structure.
Only an $AB_5$ molecule with one lone pair on the central atom, such as $BrF_5$ or $IF_5$ ($sp^3d^2$), has a square pyramidal structure.
So the statement that every $AB_5$ molecule has a square pyramid structure is not correct.
Electron-deficient molecules such as $BF_3$ and $AlCl_3$ accept electron pairs and act as Lewis acids; this is correct.
Canonical (resonating) structures are hypothetical; only the resonance hybrid has real existence; this is correct.
A multiple bond is shorter than the corresponding single bond (C-C 154 pm, C=C 134 pm, C$\equiv$C 120 pm); this is correct.
An $AB_5$ molecule with no lone pair on the central atom, such as $PCl_5$, is $sp^3d$ hybridised and has a trigonal bipyramidal structure.
Only an $AB_5$ molecule with one lone pair on the central atom, such as $BrF_5$ or $IF_5$ ($sp^3d^2$), has a square pyramidal structure.
So the statement that every $AB_5$ molecule has a square pyramid structure is not correct.
Electron-deficient molecules such as $BF_3$ and $AlCl_3$ accept electron pairs and act as Lewis acids; this is correct.
Canonical (resonating) structures are hypothetical; only the resonance hybrid has real existence; this is correct.
A multiple bond is shorter than the corresponding single bond (C-C 154 pm, C=C 134 pm, C$\equiv$C 120 pm); this is correct.