31. The correct IUPAC name of CH3CH2CH=CH2 is:
a) 1-butene
b) 2-butene
c) 1-propene
d) 2-propene
Answer: a) 1-butene
Explanation: The compound is a four-carbon chain (butene) with a double bond between the first and second carbon atoms. The correct IUPAC name is 1-butene.
32. Which of the following types of bonds is the strongest?
a) Ionic bond
b) Covalent bond
c) Hydrogen bond
d) Van der Waals forces
Answer: a) Ionic bond
Explanation: Ionic bonds are generally stronger than covalent bonds, hydrogen bonds, and Van der Waals forces because of the strong electrostatic attraction between oppositely charged ions.
33. The number of sigma (σ) bonds in benzene is:
a) 3
b) 6
c) 12
d) 9
Answer: c) 12
Explanation: In benzene (C6H6), there are six C-H sigma bonds and six C-C sigma bonds, making a total of 12 sigma bonds.
34. Which of the following has a planar structure?
a) CH4
b) NH3
c) C2H4
d) H2O
Answer: c) C2H4
Explanation: Ethylene (C2H4) has a planar structure due to the sp2 hybridization of the carbon atoms, where the π bond restricts the rotation around the carbon-carbon bond, making the entire molecule planar.
35. Which of the following molecules contains both ionic and covalent bonds?
a) HCl
b) NH4Cl
c) H2O
d) CH4
Answer: b) NH4Cl
Explanation: In ammonium chloride (NH4Cl), the ammonium ion (NH4+) forms covalent bonds within itself, and the bond between the ammonium ion and chloride ion is ionic. Therefore, NH4Cl contains both ionic and covalent bonds.
36. Which of the following compounds exhibits coordinate bonding?
a) NaCl
b) NH4+
c) CH4
d) HCl
Answer: b) NH4+
Explanation: In the ammonium ion (NH4+), nitrogen donates a lone pair of electrons to bond with an H+ ion, forming a coordinate (dative) bond.
37. The bond angle in a molecule of BF3 is:
a) 90°
b) 120°
c) 109.5°
d) 180°
Answer: b) 120°
Explanation: Boron trifluoride (BF3) has a trigonal planar geometry due to sp2 hybridization. The bond angles between the fluorine atoms are 120°.
38. Which of the following molecules has no dipole moment?
a) H2O
b) NH3
c) CH4
d) HCl
Answer: c) CH4
Explanation: Methane (CH4) is a symmetrical tetrahedral molecule, and the dipoles of the C-H bonds cancel each other out, resulting in a net dipole moment of zero.
39. Which of the following species is paramagnetic?
a) O2
b) N2
c) CO
d) F2
Answer: a) O2
Explanation: Molecular oxygen (O2) is paramagnetic due to the presence of unpaired electrons in its molecular orbitals, as predicted by molecular orbital theory.
40. Which of the following molecules has a square planar structure?
a) SF6
b) XeF4
c) PCl5
d) CH4
Answer: b) XeF4
Explanation: Xenon tetrafluoride (XeF4) has four bonding pairs and two lone pairs around the central xenon atom, resulting in a square planar structure.
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