The bond dissociation energy of B–F in BF3 is 646 kJ 1 mol⁻ whereas that of C-F in CF₄ is 515 kJ 1 mol⁻.The correct reason for higher B-F bond dissociation energy as compared to that of C-F is

• Smaller size of B-atom as compared to that of C- atom

• Stronger σ bond between B and F in BF₃ as compared to that between C and F in CF₄

• Significant pπ - pπ interaction between B and F in BF whereas there is no possibility of such 3 interaction between C and F in CF₄ 

• Significant pπ - pπ interaction between B and F in BF whereas there is no possibility of such 3 interaction between C and F in CF₄ 

Which one of the following constitutes a group of the isoelectronic species?

Which one of the following pairs of species has the same bond order?

• CN⁻ and NO⁺

• CN⁻ and CN⁺

• O₂⁻ and CN⁻

• O₂⁻ and CN⁻

Which of the following hydrogen bonds is the strongest?

• O – H …… N

• F – H …… F

• O – H ….. O

• O – H ….. O

Which of the following molecules/ions does not contain unpaired electrons?

Among the following mixtures, dipole-dipole as the major interaction is present in

• benzene and ethanol

• acetonitrile and acetone

• KCl and water

• KCl and water

Which one of the following sets of ions represents a collection of isoelectronic species?

• K⁺ , Cl^– , Ca²⁺, Sc³⁺

• Ba^2+, Sr²⁺, K⁺ , S^2–

• N^3–, O^2–, F^– , S^2–

• N^3–, O^2–, F^– , S^2–

In which of the following molecules/ions are all the bonds not equal?

• SF₄

• SiF₄

• XeF₄

• XeF₄

19.

Nickel (Z = 28) combines with a uninegative monodentate ligand X–
to form a paramagnetic complex [NiX₄ ]^{2 −}. The number of unpaired electron(s) in the nickel and geometry of this complex ion are,
respectively

• one, tetrahedral

• two, tetrahedral

• one, square planar

• one, square planar

In Fe(CO)_5, the Fe – C bond possesses 

•  π-character only

• both σ and π characters

• ionic character

• ionic character