Physical Chemistry Questions and Answers – Hydrogen Bonds, Hybrid Orbitals, and Band Theory of Solids

This set of Physical Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Hydrogen Bonds, Hybrid Orbitals, and Band Theory of Solids”.

1. At absolute zero temperature, there is a 100% para form of hydrogen and at room temperature there is 75% ortho form of hydrogen.
a) True
b) False
View Answer

Answer: a
Explanation: Since, para hydrogen has lower energy, at absolute zero, there is 100% para hydrogen and with increase in temperature proportion of para form decreases. At room temperature, hydrogen gas is mixture of 25% of para and 75% of ortho hydrogen.

2. Para hydrogen has different spins of two nuclei.
a) False
b) True
View Answer

Answer: b
Explanation: The properties of para hydrogen are a consequence of the Pauli principle. Para hydrogen is defined as molecular hydrogen in which the two hydrogen nuclei are spinning in opposite directions so that their contribution to the total angular momentum is zero.

3. Which of the following compounds has the smallest bond angle in its molecule?
a) H2O
b) H2S
c) NH3
d) SO2
View Answer

Answer: b
Explanation: As the electronegativity of the central atom decreases, bond angle decreases. In H2S, S is the central atom and it is less electronegative than oxygen. Therefore, H2S has the smallest bond angle in its molecule.

4. Why BCl3 is a planar molecule?
a) B –Cl bond is more polar
b) It has three lone pairs of electrons
c) It has two lone pairs of electrons
d) It has no lone pair of electrons
View Answer

Answer: d
Explanation: There is no lone pair on boron in BCl3 hence, no repulsion takes place and BCl3 is a planar molecule. Boron trichloride (BCl3) appears as a colorless gas with a pungent smell. It is corrosive to metals and toxic in nature.

5. How the pi bonds are formed?
a) Side to side overlap of s orbitals
b) End to end overlap of p orbitals
c) Side to side overlap of p orbitals
d) End to end overlap of p orbitals
View Answer

Answer: c
Explanation: Side to side overlap of p orbitals results in the formation of two pi molecular orbitals. The combination of out-of-phase orbitals results in an anti-bonding molecular orbital with two nodes. One contains the inter-nuclear axis and other one is perpendicular to the axis.

6. What is the type of many crystalline semi-conductors?
a) Face centered cubic
b) Body centered cubic
c) Simple cubic
d) Edge centered cubic
View Answer

Answer: a
Explanation: Many of the semi-conductors are crystals of the type face centered cubic or FCC. FCC is a type of atomic arrangement and is relatively tightly packed with atomic packing factor 0.74. FCC is defined as a cubic lattice with the face positions fully equivalent to each of the eight corners.

7. What carries the charge in semiconductors?
a) Holes only
b) Electrons and holes both
c) Electrons only
d) There is no charge carrier in semiconductors
View Answer

Answer: b
Explanation: In semi-conductors, the charge carriers are electrons and holes. Semiconductors are of two types, n-type semi-conductors and p-type semi-conductors. In n-type semi-conductors, the charge carriers are electrons whereas in p-type semiconductors, the charge carriers are holes.

8. Which of the following represents the energy needed to magnetize and demagnetize?
a) Hysteresis curve
b) Hysteresis loop
c) Hysteresis loop area
d) Straight line
View Answer

Answer: c
Explanation: The area of the loop is a measure of the energy needed to magnetize and demagnetize each cycle. This is the energy required to do work against internal friction of the domains. This work is done against friction, is dissipated as heat. It is called hysteresis loss.

9. Which of the following has holes in them?
a) Conductors
b) Semi-conductors
c) Insulators
d) Conductors, insulators and semi-conductors
View Answer

Answer: b
Explanation: Semi-conductors have holes in them. Holes are formed when the electrons in atoms move out of the valence band into conduction band. Holes play an important role in the operation of semi-conductor devices such as transistors, diodes and integrated circuits.

10. Is the following statement true?
Statement: On the basis of band theory of solids the semi-conductors have a completely filled valence band, a partially filled conduction band and a narrow forbidden band.
a) Statement is false
b) Statement is true
View Answer

Answer: b
Explanation: The given statement is true because semi-conductors are classified by the fully occupied valence band and unoccupied conduction band. With the small band gap in between these two bands, it takes a certain amount of energy to excite the electrons from the valence to conduction band.

Sanfoundry Global Education & Learning Series – Physical Chemistry.

To practice all areas of Physical Chemistry, here is complete set of Multiple Choice Questions and Answers.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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