Question: 86. Identify the correct answer.
(1) Three resonance structures can be drawn for ozone
(2) \mathrm{BF}_{3} has non-zero dipole moment
(3) Dipole moment of \mathrm{NF}_{3} is greater than that of \mathrm{NH}_{3}
(4) Three canonical forms can be drawn for \mathrm{CO}_{3}^{2-} ion.
Answer: Option (4)
Explanation:
Ozone has two equivalent resonance structures, not three, so statement (1) is incorrect.
\mathrm{BF}_{3} is a trigonal planar molecule with symmetrical arrangement of bonds,
so the individual bond dipoles cancel each other and the net dipole moment is zero.
Hence statement (2) is incorrect.
The dipole moment of \mathrm{NH}_{3} is greater than that of
\mathrm{NF}_{3} because in \mathrm{NF}_{3},
the bond dipoles oppose the lone pair dipole, reducing the net dipole moment.
Therefore, statement (3) is incorrect.
The carbonate ion \mathrm{CO}_{3}^{2-} has three equivalent resonance (canonical) structures due to the delocalization of the double bond among the three oxygen atoms.
Hence, the correct statement is option (4).