51. Which of the following molecules is linear?
a) H2O
b) NH3
c) C2H2
d) SO2
Answer: c) C2H2
Explanation: Ethyne (C2H2) is a linear molecule due to sp hybridization of the carbon atoms, with a bond angle of 180°.
52. In which of the following molecules are all atoms sp2 hybridized?
a) CH4
b) BF3
c) C2H6
d) NH3
Answer: b) BF3
Explanation: In boron trifluoride (BF3), the boron atom and all the fluorine atoms are sp2 hybridized, resulting in a trigonal planar geometry.
53. Which of the following molecules has a seesaw shape?
a) SF4
b) PCl5
c) XeF4
d) CH4
Answer: a) SF4
Explanation: In sulfur tetrafluoride (SF4), the central sulfur atom has four bonding pairs and one lone pair, resulting in a seesaw shape according to VSEPR theory.
54. Which of the following species is diamagnetic?
a) O2
b) NO
c) N2
d) B2
Answer: c) N2
Explanation: Molecular nitrogen (N2) is diamagnetic because all of its electrons are paired, while O2 and NO have unpaired electrons and are paramagnetic.
55. The formal charge on the oxygen atom in the carbonate ion (CO3^2-) is:
a) 0
b) -1
c) +1
d) -2
Answer: a) 0
Explanation: In the carbonate ion, the formal charge on each oxygen atom is 0, as the charge is delocalized over the resonance structures of the ion.
56. Which of the following species has a bond order of 2.5?
a) O2
b) CO
c) NO
d) N2
Answer: c) NO
Explanation: Nitric oxide (NO) has a bond order of 2.5, as it has an odd number of electrons, with one unpaired electron in a bonding molecular orbital.
57. Which of the following exhibits sp3d hybridization?
a) PCl5
b) SF6
c) XeF4
d) CH4
Answer: a) PCl5
Explanation: Phosphorus in PCl5 undergoes sp3d hybridization, resulting in a trigonal bipyramidal structure with 90° and 120° bond angles.
58. Which of the following has the smallest bond angle?
a) CH4
b) NH3
c) H2O
d) CO2
Answer: c) H2O
Explanation: Water (H2O) has the smallest bond angle of approximately 104.5° due to the strong lone pair-lone pair repulsion, compared to NH3 (107°), CH4 (109.5°), and CO2 (180°).
59. Which of the following molecules has a square pyramidal geometry?
a) SF6
b) PCl5
c) IF5
d) XeF4
Answer: c) IF5
Explanation: In iodine pentafluoride (IF5), the central iodine atom has five bonding pairs and one lone pair, resulting in a square pyramidal geometry.
60. The correct IUPAC name of the compound (CH3)2CHCH2CH3 is:
a) 3-methylpentane
b) 2-methylpentane
c) 2-methylbutane
d) 3-methylbutane
Answer: c) 2-methylbutane
Explanation: The longest chain contains four carbon atoms, and a methyl group is attached to the second carbon atom. Therefore, the correct IUPAC name is 2-methylbutane.
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