12. What is the bond order of O2 molecule in its ground state?
a) 1
b) 2
c) 3
d) 0
Answer: b) 2
Explanation: The bond order can be calculated by using molecular orbital theory. For O2, the bond order is given by the formula:
Bond order = (Number of bonding electrons – Number of anti-bonding electrons) / 2.
For O2, the bond order comes out to be 2, indicating a double bond between the oxygen atoms.
13. Which of the following statements is true for carbon dioxide (CO2)?
a) It has a bent shape
b) It has a linear shape
c) It has a pyramidal shape
d) It has a square planar shape
Answer: b) It has a linear shape
Explanation: CO2 has two double bonds between the carbon and oxygen atoms, and no lone pairs on the central carbon atom. The molecule has a linear shape with a bond angle of 180°.
14. Which of the following compounds exhibits sp hybridization?
a) BeCl2
b) BF3
c) CH4
d) NH3
Answer: a) BeCl2
Explanation: In BeCl2, beryllium forms two bonds with chlorine. To accommodate these bonds, beryllium undergoes sp hybridization, resulting in a linear structure.
15. Which of the following molecules does not have a permanent dipole moment?
a) H2O
b) CH4
c) NH3
d) HCl
Answer: b) CH4
Explanation: Methane (CH4) is a symmetrical molecule with a tetrahedral geometry, and the dipole moments of the C-H bonds cancel each other out. Hence, CH4 does not have a permanent dipole moment.
16. The bond angle in NH3 is less than 109.5° because:
a) Lone pairs repel bonding pairs more strongly than bonding pairs repel each other.
b) NH3 has no lone pairs.
c) NH3 has a square planar geometry.
d) The bond angle in NH3 is exactly 109.5°.
Answer: a) Lone pairs repel bonding pairs more strongly than bonding pairs repel each other.
Explanation: In ammonia (NH3), the nitrogen atom has one lone pair of electrons and three bond pairs. The lone pair exerts greater repulsion on the bonding pairs, reducing the bond angle to approximately 107°.
17. Which of the following types of bonds is present in the ammonium ion (NH4+)?
a) Ionic bond
b) Covalent bond
c) Dative bond
d) Metallic bond
Answer: c) Dative bond
Explanation: In the ammonium ion (NH4+), the nitrogen atom donates a lone pair of electrons to form a bond with a proton (H+), creating a dative or coordinate bond. Additionally, the other bonds are regular covalent bonds.
18. The number of sigma (σ) and pi (π) bonds in ethyne (C2H2) are:
a) 3 sigma and 1 pi bond
b) 2 sigma and 2 pi bonds
c) 3 sigma and 2 pi bonds
d) 1 sigma and 3 pi bonds
Answer: c) 3 sigma and 2 pi bonds
Explanation: Ethyne (C2H2) has a triple bond between the two carbon atoms. A triple bond consists of 1 sigma bond and 2 pi bonds. Additionally, each carbon forms a sigma bond with a hydrogen atom. Therefore, there are 3 sigma bonds and 2 pi bonds in total.
19. Which of the following molecules has a non-zero dipole moment?
a) CO2
b) CHCl3
c) CCl4
d) BF3
Answer: b) CHCl3
Explanation: CHCl3 (chloroform) has a tetrahedral structure, but the asymmetrical arrangement of atoms (one hydrogen and three chlorine atoms) results in a net dipole moment. Other options like CO2 and CCl4 are symmetrical and have no net dipole moment.
20. The shape of the SF6 molecule is:
a) Tetrahedral
b) Octahedral
c) Square planar
d) Trigonal bipyramidal
Answer: b) Octahedral
Explanation: Sulfur hexafluoride (SF6) has six bonding pairs of electrons around the central sulfur atom. These six pairs arrange themselves in an octahedral geometry, with bond angles of 90°.
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