Free Chemical Bonding MCQs with Answers

41. In propene pi-bond is formed by sideway overlap of:

• A. s-orbitals
• B. p-orbitals
• C. sp3 hybrid orbitals
• D. sp2 hybrid orbitals

Explanation: Each doubly bonded carbon uses three sp2 hybrids for its sigma bonds and keeps one unhybridised p orbital, and the sideways overlap of those two p orbitals above and below the plane forms the pi bond. Hybrid orbitals point along the internuclear axis and so can only make sigma bonds. This is why rotation about the double bond is blocked.

42. Molecules having one lone pair and three bond pairs have geometrical shape

• A. Bent or angular
• B. Trigonal
• C. Trigonal pyramidal
• D. Trigonal planar

Explanation: Four regions of electron density arrange themselves tetrahedrally, but only the three bonded atoms are visible, so the shape is a pyramid, as in ammonia with its bond angle of about 107 degrees. Trigonal planar at 120 degrees would require three bond pairs and no lone pair, as in boron trifluoride, which is the trap here. A bent shape comes from two bond pairs with two lone pairs, as in water.

43. The theories which explain the formation of sigma and pi bond are EXCEPT:

• A. MOT
• B. VBT
• C. VSEPR
• D. CFT

Explanation: Crystal field theory deals with how the d orbitals of a transition metal ion are split by the surrounding ligands, so it explains colour and magnetic behaviour in complexes rather than the formation of sigma and pi bonds. Valence bond theory and molecular orbital theory both describe those bonds directly through orbital overlap. VSEPR predicts shape from electron pair repulsion and so also concerns bonding.

44. Correct arrangement of orbital according to size of hybridized orbitals?

• A. sp > sp2 > sp3
• B. sp3 > sp > sp2
• C. sp2 > sp > sp3
• D. sp3 > sp2 > sp

Explanation: The greater the s character, the closer the orbital is held to the nucleus and the smaller it is, and s character rises from 25 per cent in sp3 through 33 per cent in sp2 to 50 per cent in sp. So sp3 is the largest and sp the smallest. The same trend explains why an sp carbon holds its bonding electrons most tightly, making terminal alkynes weakly acidic.