States of Matter — 50 MCQs

1. The SI unit of pressure is:

1. atm
2. bar
3. Pascal (Pa) ✅
4. Torr

2. Boyle’s law relates:

1. Pressure & Temperature
2. Pressure & Volume ✅
3. Volume & Temperature
4. Mass & Volume

3. Charles’s law states (at constant P):

1. V ∝ 1/T
2. V ∝ T ✅
3. P ∝ V
4. P ∝ T

4. Avogadro’s law states:

1. Equal masses contain equal molecules
2. Equal volumes at same T & P contain equal molecules ✅
3. Equal pressures mean equal moles
4. Equal temperatures mean equal mass

5. Ideal gas equation is:

1. PV = k
2. PV = nRT ✅
3. P/T = k
4. V = RT

6. The value of R (gas constant) in SI units is approximately:

1. 8.314 J·mol⁻¹·K⁻¹ ✅
2. 0.0821 L·atm·K⁻¹·mol⁻¹
3. 1.0 Pa·m³
4. 22.4 L·mol⁻¹

7. At constant temperature and moles, if volume doubles, pressure will:

1. double
2. halve ✅
3. remain same
4. quadruple

8. The molar volume of an ideal gas at STP (0°C, 1 atm) is:

1. 11.2 L
2. 22.4 L ✅
3. 24.0 L
4. 44.8 L

9. Real gases deviate most from ideal behavior at:

1. Low pressure, high temperature
2. High pressure, low temperature ✅
3. High pressure, high temperature
4. Low pressure, low temperature

10. Van der Waals equation corrects the ideal gas law for:

1. Quantum effects
2. Finite molecular volume and intermolecular forces ✅
3. Catalysis
4. Ionization

11. The van der Waals constant ‘a’ corrects for:

1. Molecular volume
2. Attractive forces between molecules ✅
3. Repulsive forces only
4. Temperature dependence

12. The van der Waals constant ‘b’ accounts for:

1. Attractive forces
2. Finite volume of molecules (excluded volume) ✅
3. Ionization energy
4. Compressibility

13. Compressibility factor Z = PV / nRT. For an ideal gas Z =:

1. 0
2. 1 ✅
3. >1 always
4. <1 always

14. Dalton’s law of partial pressures states:

1. Total pressure equals average of partial pressures
2. Total pressure equals sum of partial pressures of components ✅
3. Partial pressure equals mole fraction × temperature
4. Partial pressures are independent of composition

15. Graham’s law relates to:

1. Solubility of gases
2. Rate of effusion/diffusion ∝ 1/√(molar mass) ✅
3. Vapor pressure vs temperature
4. Compressibility

16. Which process describes gas molecules escaping through a small hole into vacuum?

1. Diffusion
2. Effusion ✅
3. Osmosis
4. Sublimation

17. Root mean square (rms) speed of gas molecules increases with:

1. Increasing molar mass
2. Increasing temperature ✅
3. Decreasing temperature
4. Increasing pressure only

18. The kinetic molecular theory assumes gas molecules:

1. Have strong intermolecular attractions
2. Are in constant random motion and collisions are elastic ✅
3. Occupy most of the gas volume
4. Are stationary

19. Mean free path of gas molecules is:

1. Distance between gas and container wall
2. Average distance traveled between collisions ✅
3. Average molecular diameter
4. Path length of diffusion

20. Vapor pressure of a liquid depends mainly on:

1. Surface area only
2. Volume of liquid
3. Temperature ✅
4. Container shape

21. Boiling point of a liquid is the temperature at which:

1. Vaporization ceases
2. Vapor pressure equals external pressure ✅
3. Vapor pressure is minimum
4. Liquid freezes

22. Critical temperature (Tc) is:

1. Temperature where vapor pressure is zero
2. Above which gas cannot be liquefied by pressure alone ✅
3. Temperature of absolute zero
4. Where triple point occurs

23. At the critical point of a substance:

1. Solid, liquid & gas coexist
2. Liquid and gas phases become indistinguishable ✅
3. Only solid exists
4. Vapor pressure is zero

24. Liquefaction of gases is easier when:

1. Temperature is well above Tc
2. Temperature is below critical temperature and pressure applied ✅
3. Molar mass is very low always
4. Gas is monatomic only

25. Joule-Thomson effect describes:

1. Change in temperature with volume at constant pressure
2. Temperature change of a real gas during throttling at constant enthalpy ✅
3. Work done by gas in reversible process
4. Diffusion rate

26. A positive Joule-Thomson coefficient means gas cools upon expansion at constant enthalpy. Which gas at room temperature shows cooling on throttling?

1. Helium
2. Nitrogen (and most real gases below inversion temperature) ✅
3. Hydrogen
4. Ideal gases (always)

27. Which intermolecular force is strongest among these in water?

1. London dispersion
2. Dipole–dipole
3. Hydrogen bonding ✅
4. Ionic bonding (in pure water)

28. Which state has highest intermolecular forces (generally)?

1. Gas
2. Liquid
3. Solid ✅
4. Plasma

29. Sublimation is the transition from:

1. Solid → Liquid
2. Liquid → Gas
3. Solid → Gas without passing liquid ✅
4. Gas → Solid via liquid

30. Triple point of a substance is:

1. When three solids form
2. Temperature & pressure where solid, liquid & gas coexist in equilibrium ✅
3. When three gases mix
4. Where critical point occurs

31. The Clausius-Clapeyron equation relates:

1. Pressure and volume of gases
2. Vapor pressure and temperature (enthalpy of vaporization) ✅
3. Gibbs free energy and entropy only
4. Molar mass and temperature

32. For an ideal gas, internal energy depends on:

1. Volume only
2. Temperature only ✅
3. Pressure only
4. Temperature and volume both

33. Boyle temperature is that temperature at which:

1. Gas is ideal at all pressures
2. Second virial coefficient = 0 (gas shows ideal behavior over range) ✅
3. Gas liquefies spontaneously
4. Compressibility factor = 0

34. Degree of freedom (translational) for a monoatomic gas per molecule is:

1. 1
2. 2
3. 3 ✅
4. 6

35. Heat capacity at constant volume (Cv) for a monoatomic ideal gas (per mole, classical) is:

1. 3R
2. 1.5 R
3. 3/2 R ✅
4. 5/2 R

36. Dalton’s law can be applied to gas mixtures because partial pressure of a gas depends on:

1. Its identity only
2. Its mole fraction and total pressure ✅
3. Volume only
4. Temperature only

37. Which gas law is represented by P1/T1 = P2/T2 (at constant V)?

1. Boyle’s law
2. Gay-Lussac’s law (pressure-temperature relation) ✅
3. Charles’s law
4. Avogadro’s law

38. The ratio of rates of effusion of gases A and B is √(M_B / M_A). This is from:

1. Dalton’s law
2. Graham’s law ✅
3. Henry’s law
4. Raoult’s law

39. Henry’s law relates:

1. Vapor pressure and temperature
2. Vapor pressure and mole fraction
3. Solubility of gas in liquid ∝ partial pressure of gas over liquid ✅
4. Effusion rate and molar mass

40. Which statement about ideal gases is FALSE?

1. Molecules have negligible volume
2. Collisions are perfectly elastic
3. Attractive forces between molecules are significant ✅ (this is FALSE for ideal gas)
4. Obey PV = nRT

41. The molar mass of a gas can be measured experimentally using:

1. Boyle’s law only
2. Graham’s law or from density and ideal gas law ✅
3. Avogadro’s law only
4. Clausius-Clapeyron only

42. In vapor–liquid equilibrium, increasing temperature generally:

1. Decreases vapor pressure
2. Increases vapor pressure ✅
3. Has no effect
4. Decreases boiling point

43. Surface tension of a liquid generally:

1. Increases with temperature
2. Decreases with temperature ✅
3. Is independent of temperature
4. Is maximum at boiling point

44. Viscosity of a liquid typically:

1. Decreases with decreasing intermolecular forces
2. Decreases with increasing temperature (for liquids) ✅
3. Increases with temperature always
4. Is same for all liquids

45. Which gas law best describes behavior when n and T are constant?

1. Charles’s law
2. Boyle’s law ✅
3. Avogadro’s law
4. Gay-Lussac’s law

46. The evaporation cooling effect occurs because:

1. All molecules gain energy during evaporation
2. High-energy molecules escape, lowering average kinetic energy of remaining liquid ✅
3. Pressure increases
4. Temperature of surroundings rises

47. Which is true about condensation?

1. Endothermic process
2. Exothermic process (releases heat) ✅
3. Requires continuous heat input
4. Occurs only under vacuum

48. The law that relates vapor pressure of a solution to mole fraction of solvent is:

1. Henry’s law
2. Raoult’s law ✅
3. Dalton’s law
4. Boyle’s law

49. Mean kinetic energy of gas molecules is proportional to:

1. Pressure only
2. Absolute temperature (T) ✅
3. Volume only
4. Molar mass