Intermolecular Forces & Properties
About Chemistry MCQs
Chemistry is the scientific study of the properties and behavior of matter. It is a fundamental subject for medical and engineering entry tests, as well as a standard component of science exams. Understanding chemical reactions, the periodic table, and molecular structures is key to success in this subject.
Topics Covered in This Category
- Physical Chemistry: Atomic structure, chemical bonding, thermodynamics, and equilibrium.
- Organic Chemistry: Hydrocarbons, functional groups, and reaction mechanisms.
- Inorganic Chemistry: Transition metals, coordination compounds, and the periodic table.
- Analytical Chemistry: Titrations, spectroscopy, and qualitative analysis.
How to Master Chemistry MCQs
Chemistry requires a balance of understanding and memorization. Keep a notebook of chemical reactions and their conditions. Practice numerical problems daily. For MCQs, pay close attention to units, signs, and exceptions to general rules, as examiners often use these to create trick questions.
All Questions for: Intermolecular Forces & Properties
Question 1: Which intermolecular force is the strongest?
- A Hydrogen bonding
- B London dispersion forces
- C Dipole-dipole interactions
- D Ion-induced dipole interactions
Explanation: Hydrogen bonding is the strongest intermolecular force (typically 5–40 kJ/mol), arising when H is bonded to N, O, or F and interacts with a lone pair on an electronegative atom.
Question 2: London dispersion forces increase with:
- A Increasing molecular size and polarizability
- B Increasing bond strength
- C Higher temperature
- D Decreasing molecular mass
Explanation: London dispersion forces arise from instantaneous dipoles and increase with electron count (molecular size/polarizability). Larger molecules have stronger dispersion forces.
Question 3: Hydrogen bonding can occur when hydrogen is covalently bonded to:
- A N, O, or F
- B C, Si, or Ge
- C Cl, Br, or I
- D Any atom
Explanation: Hydrogen bonds form when H is bonded to a strongly electronegative, small atom: nitrogen, oxygen, or fluorine.
Question 4: Water has a higher boiling point than H₂S primarily because of:
- A Hydrogen bonding
- B Larger molecular mass
- C Higher molecular symmetry
- D Covalent network structure
Explanation: Water forms strong hydrogen bonds, while H₂S only experiences weaker dipole-dipole and dispersion forces because sulfur is less electronegative than oxygen.
Question 5: Which of the following has the highest boiling point?
- A H₂O
- B H₂S
- C H₂Se
- D H₂Te
Explanation: H₂O forms extensive hydrogen bonds, giving it a boiling point (100°C) much higher than H₂S, H₂Se, or H₂Te despite its lower molar mass.
Question 6: Which is the correct order of boiling points?
- A H₂O > H₂Te > H₂Se > H₂S
- B H₂S > H₂Se > H₂Te > H₂O
- C H₂O > H₂S > H₂Se > H₂Te
- D H₂Te > H₂Se > H₂S > H₂O
Explanation: Stronger intermolecular forces → higher boiling point. H₂O (H-bonding) > H₂Te (dipole + dispersion) > H₂Se > H₂S.
Question 7: Which type of intermolecular force is present in ALL molecules, polar or nonpolar?
- A London dispersion forces
- B Hydrogen bonding
- C Dipole-dipole interactions
- D Ion-dipole interactions
Explanation: London dispersion forces arise from instantaneous fluctuations in electron density and are universal — present in all atoms and molecules.
Question 8: Which of the following molecules would have the strongest London dispersion forces?
- A I₂
- B F₂
- C Cl₂
- D Br₂
Explanation: Among the halogens (F₂, Cl₂, Br₂, I₂), iodine (I₂) has the largest and most polarizable electron cloud, leading to the strongest dispersion forces.
Question 9: Surface tension in liquids is caused by:
- A Net inward force on surface molecules due to unbalanced attractions
- B Outward pressure from the gas phase
- C Hydrogen bonding only
- D Ionic interactions only
Explanation: Molecules at the surface have fewer neighboring molecules, so they experience a net inward pull. This unbalanced force creates surface tension.
Question 10: Viscosity of a liquid increases with:
- A Stronger intermolecular forces and larger molecular size
- B Higher temperature
- C Smaller molecular size
- D Weaker intermolecular forces
Explanation: Stronger intermolecular forces and larger molecular size increase viscosity by making it harder for molecules to slide past each other.
Question 11: The vapor pressure of a liquid is determined by:
- A Strength of intermolecular forces and temperature
- B Volume of the container only
- C Surface area only
- D Atomic mass only
Explanation: Vapor pressure depends on the strength of intermolecular forces and temperature. Weaker forces and higher temperatures increase vapor pressure.
Question 12: Which of the following is NOT an intermolecular force?
- A Ionic bond
- B London dispersion force
- C Dipole-dipole interaction
- D Hydrogen bond
Explanation: Ionic bonds are intramolecular (they occur within an ionic compound). London dispersion, dipole-dipole, and hydrogen bonds are all intermolecular forces.
Question 13: Molecules of a gas are characterized by:
- A Weak intermolecular forces and large distances between molecules
- B Strong intermolecular forces and fixed positions
- C Ordered crystalline arrangement
- D High density and low compressibility
Explanation: In a gas, intermolecular forces are negligible and molecules are far apart, moving rapidly and randomly.
Question 14: The critical temperature of a gas is:
- A The temperature above which a gas cannot be liquefied by pressure alone
- B The temperature at which a gas becomes an ideal gas
- C The boiling point of a liquid
- D The freezing point of a gas
Explanation: Above the critical temperature, a gas cannot be liquefied regardless of pressure. It represents the temperature at which the gas and liquid phases become indistinguishable.
Question 15: Which of the following liquids would have the highest vapor pressure at room temperature?
- A Diethyl ether
- B Water
- C Ethanol
- D Ethylene glycol
Explanation: Higher vapor pressure = weaker intermolecular forces. Diethyl ether has only weak dipole-dipole and dispersion forces (no hydrogen bonding), so it is more volatile than water, ethanol, or ethylene glycol (which form H-bonds).
Question 16: Adhesive forces are:
- A Forces between molecules of different substances
- B Forces between molecules of the same substance
- C Forces within a molecule
- D Nuclear forces
Explanation: Adhesive forces are attractive forces between molecules of DIFFERENT substances (e.g., water and glass). Cohesive forces are between identical molecules.
Question 17: Capillary action in a narrow tube is due to:
- A Combined effect of adhesive and cohesive forces
- B Gravity alone
- C Atmospheric pressure alone
- D Only cohesive forces
Explanation: Capillary action results from the combination of adhesive forces (between liquid and tube) and cohesive forces (within the liquid). When adhesion > cohesion (as with water in glass), the liquid rises.
Question 18: Mercury does not wet glass because:
- A Cohesive forces exceed adhesive forces with glass
- B Its boiling point is too low
- C It has no intermolecular forces
- D Its density is too low
Explanation: Mercury's cohesive forces are stronger than its adhesive forces with glass, so it forms a convex meniscus and is pushed down in a capillary tube.
Question 19: Which of the following exhibits hydrogen bonding?
- A HF
- B HCl
- C HBr
- D HI
Explanation: HF can form hydrogen bonds because H is attached to highly electronegative F. HCl, HBr, and HI have progressively weaker hydrogen bonding (essentially none).
Question 20: Ion-dipole interactions are important in:
- A Solutions of ionic compounds in polar solvents
- B Nonpolar gases
- C Pure covalent crystals
- D Metallic solids
Explanation: Ion-dipole interactions occur between an ion and a polar molecule — for example, Na⁺ surrounded by water molecules in solution. These interactions are key to dissolution of ionic salts in water.
Question 21: Which of the following has the lowest boiling point?
- A CH₄
- B SiH₄
- C GeH₄
- D SnH₄
Explanation: Small, nonpolar molecules have only weak London dispersion forces. Among CH₄, SiH₄, GeH₄, SnH₄, methane is smallest and has the weakest dispersion forces — lowest boiling point.
Question 22: Which of the following statements about hydrogen bonding is FALSE?
- A Hydrogen bonds are as strong as covalent bonds
- B Hydrogen bonding affects boiling points of water and ammonia
- C Hydrogen bonds form when H is bonded to N, O, or F
- D Hydrogen bonding explains the structure of DNA and proteins
Explanation: Hydrogen bonds are much weaker than covalent bonds (5–40 kJ/mol vs 150–1000+ kJ/mol). They are attractions between molecules, not true chemical bonds in the covalent sense.
Question 23: The anomalous high boiling point of water compared to other hydrides is primarily due to:
- A Each water molecule can form up to four hydrogen bonds
- B Water has a very high molecular mass
- C Water is nonpolar
- D Water has weak intermolecular forces
Explanation: Water forms up to 4 hydrogen bonds per molecule (two as donor, two as acceptor), resulting in a highly extensive and strong hydrogen-bonding network.
Question 24: Which has the highest boiling point among the following?
- A I₂
- B F₂
- C Cl₂
- D Br₂
Explanation: Larger nonpolar molecules have stronger London dispersion forces. I₂ has the largest electron cloud and highest molecular mass among F₂, Cl₂, Br₂, I₂, giving the strongest dispersion forces and highest boiling point.
Question 25: The meniscus of water in a glass tube is concave because:
- A Adhesive forces with glass are stronger than cohesive forces
- B Cohesive forces are stronger than adhesive forces
- C Water has a low surface tension
- D Gravity pulls water upward
Explanation: When adhesion (water-glass) is stronger than cohesion (water-water), water is pulled up along the walls of the tube, producing a concave meniscus.