21. Which of the following exhibits resonance?
a) CH4
b) H2O
c) O3
d) NH3
Answer: c) O3
Explanation: Ozone (O3) exhibits resonance, as it can be represented by two equivalent Lewis structures in which the placement of the double bond and single bond between the oxygen atoms alternates.
22. Which of the following molecules has sp2 hybridization at the central atom?
a) C2H2
b) C2H4
c) C2H6
d) CH4
Answer: b) C2H4
Explanation: In ethylene (C2H4), each carbon atom forms three sigma bonds (two with hydrogen and one with another carbon atom) and one π bond. Therefore, the carbon atoms are sp2 hybridized.
23. The geometry of a molecule with three bonding pairs and one lone pair on the central atom is:
a) Linear
b) Tetrahedral
c) Trigonal pyramidal
d) Square planar
Answer: c) Trigonal pyramidal
Explanation: A molecule with three bonding pairs and one lone pair, such as NH3, adopts a trigonal pyramidal geometry due to the lone pair-bond pair repulsion, which distorts the shape from being tetrahedral.
24. Which of the following is the correct IUPAC name of the compound CH3CH(CH3)CH2CH3?
a) 3-methylbutane
b) 2-methylbutane
c) Isopentane
d) 1-methylpropane
Answer: b) 2-methylbutane
Explanation: The longest chain contains four carbon atoms (butane), and a methyl group is attached to the second carbon atom. Hence, the correct IUPAC name is 2-methylbutane.
25. Which of the following compounds has the highest bond order?
a) N2
b) O2
c) F2
d) NO
Answer: a) N2
Explanation: Nitrogen (N2) has a bond order of 3 (a triple bond), while oxygen (O2) has a bond order of 2, fluorine (F2) has a bond order of 1, and nitric oxide (NO) has a bond order between 2 and 3. Hence, N2 has the highest bond order.
26. Which of the following molecules has sp3 hybridization at the central atom?
a) C2H2
b) C2H4
c) CH4
d) CO2
Answer: c) CH4
Explanation: In methane (CH4), carbon forms four sigma bonds with four hydrogen atoms. Carbon undergoes sp3 hybridization to form four equivalent sp3 hybrid orbitals, resulting in a tetrahedral geometry.
27. The bond angle in water (H2O) is approximately:
a) 90°
b) 104.5°
c) 109.5°
d) 120°
Answer: b) 104.5°
Explanation: In water, the oxygen atom has two lone pairs and two bond pairs. The lone pair-lone pair repulsion causes the bond angle to reduce from the ideal tetrahedral angle of 109.5° to about 104.5°, giving water its bent shape.
28. Which of the following is the correct IUPAC name of the compound CH3CH2COOH?
a) Ethanoic acid
b) Propanoic acid
c) Butanoic acid
d) Methanoic acid
Answer: b) Propanoic acid
Explanation: The compound has three carbon atoms, with the carboxyl group (-COOH) attached to the first carbon atom. Therefore, the correct IUPAC name is propanoic acid.
29. Which of the following has a bond order of 1?
a) O2
b) H2
c) F2
d) N2
Answer: c) F2
Explanation: In fluorine (F2), the bond order is 1, indicating a single bond between the two fluorine atoms. This is because each fluorine atom shares one electron with the other to complete its octet.
30. Which of the following molecules has a trigonal pyramidal shape?
a) BF3
b) H2O
c) NH3
d) CH4
Answer: c) NH3
Explanation: Ammonia (NH3) has three bonding pairs and one lone pair of electrons around the nitrogen atom, which gives it a trigonal pyramidal shape. The lone pair-bond pair repulsion slightly reduces the bond angle from 109.5°.
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