FSc Pre-Medical Chemistry Gases — Set 3

1. Question 1

   Q1. Which gas shows the greatest deviation from ideal gas behavior at high pressure due to strong intermolecular attractions?

   • A) H2
   • B) N2
   • C) CH4
   • D) NH3

   Answer: NH3

   Explanation: NH3 has hydrogen bonding, causing significant deviation. H2 and CH4 have weaker intermolecular forces.

2. Question 2

   Q2. Which gas has the lowest critical temperature and cannot be liquefied at room temperature under any pressure?

   • A) CO2
   • B) H2
   • C) O2
   • D) N2

   Answer: H2

   Explanation: H2’s critical temperature is -239.9°C. CO2 and O2 can be liquefied at room temperature with sufficient pressure.

3. Question 3

   Q3. Which gas exhibits anomalous behavior by decreasing solubility in water when temperature decreases?

   • A) CO2
   • B) O2
   • C) N2
   • D) CH4

   Answer: CO2

   Explanation: CO2 solubility decreases with cooling due to reverse Henry’s law behavior. O2 follows normal solubility trends.

4. Question 4

   Q4. Which gas has the highest viscosity at 25°C despite having low molecular mass?

   • A) O2
   • B) N2
   • C) CO2
   • D) H2

   Answer: CO2

   Explanation: CO2’s larger size increases collision frequency. N2 and O2 have simpler molecular structures.

5. Question 5

   Q5. Which gas’s liquid form has the lowest surface tension compared to other common liquid gases?

   • A) NH3
   • B) CH4
   • C) CO2
   • D) H2O

   Answer: CH4

   Explanation: CH4’s weak van der Waals forces reduce surface tension. NH3 has hydrogen bonding, increasing surface tension.

6. Question 6

   Q6. Which gas shows negative deviation from Graham’s law during effusion due to its molecular shape?

   • A) O2
   • B) H2O
   • C) CO2
   • D) CH4

   Answer: CH4

   Explanation: CH4’s spherical shape increases collision frequency. O2 and H2O are linear or polar.

7. Question 7

   Q7. Which gas has the highest thermal conductivity at room temperature despite not being the lightest?

   • A) H2
   • B) He
   • C) O2
   • D) CO2

   Answer: H2

   Explanation: H2’s lightness allows faster energy transfer. CO2’s mass reduces thermal conductivity.

8. Question 8

   Q8. Which gas forms a solid (dry ice) directly under pressure at room temperature without passing through a liquid phase?

   • A) NH3
   • B) CO2
   • C) SO2
   • D) CH4

   Answer: CO2

   Explanation: CO2’s sublimation at 1 atm is due to its phase diagram. NH3 liquefies before solidifying.

9. Question 9

   Q9. Which gas exhibits positive Joule-Thomson coefficient at room temperature, causing cooling upon expansion?

   • A) H2
   • B) He
   • C) CO2
   • D) N2

   Answer: CO2

   Explanation: CO2 cools during expansion. H2 and He warm due to their molecular properties.

10. Question 10

    Q10. Which gas has the lowest compressibility factor (Z) at high pressure due to negligible intermolecular attractions?

    • A) H2
    • B) O2
    • C) CH4
    • D) NH3

    Answer: H2

    Explanation: H2’s weak attractions lead to Z < 1. NH3’s attractions cause Z > 1 at high pressure.

11. Question 11

    Q11. Which gas deviates most from the inverse pressure-volume relationship at low pressures?

    • A) N2
    • B) CO2
    • C) H2
    • D) He

    Answer: CO2

    Explanation: CO2’s strong intermolecular forces cause deviation. H2 and He behave closer to ideal.

12. Question 12

    Q12. Which gas shows the smallest change in volume when cooled from 100°C to 0°C under constant pressure?

    • A) He
    • B) O2
    • C) CO2
    • D) NH3

    Answer: CO2

    Explanation: CO2’s intermolecular attractions reduce volume contraction. He follows Charles’s law closely.

13. Question 13

    Q13. Which gas has the highest solubility in water at 25°C despite not reacting with it?

    • A) O2
    • B) N2
    • C) CO2
    • D) CH4

    Answer: CO2

    Explanation: CO2 dissolves via physical absorption. O2 and N2 have lower solubility.

14. Question 14

    Q14. Which gas exhibits the greatest increase in viscosity with temperature?

    • A) H2
    • B) N2
    • C) CO2
    • D) O2

    Answer: CO2

    Explanation: CO2’s larger size increases collision frequency. H2’s viscosity increases less rapidly.

15. Question 15

    Q15. Which gas has the highest molar volume at STP when measured experimentally under real conditions?

    • A) H2
    • B) CO2
    • C) O2
    • D) N2

    Answer: H2

    Explanation: H2’s weak intermolecular forces expand its volume. CO2 and O2 compress more.

16. Question 16

    Q16. Which gas shows anomalous expansion by decreasing in volume when heated at constant pressure below -234°C?

    • A) He
    • B) O2
    • C) CO2
    • D) H2

    Answer: H2

    Explanation: H2’s expansion at low temperatures is anomalous. He and O2 follow normal expansion.

17. Question 17

    Q17. A person inhales helium, and their voice becomes higher pitched. What occurs in the lungs to cause this change?

    • A) Increased partial pressure of oxygen
    • B) Decreased viscosity of air
    • C) Increased solubility of helium in blood
    • D) Swelling of vocal cords

    Answer: Increased solubility of helium in blood

    Explanation: Increased solubility of helium in blood causes diffusion into vocal cords, reducing their mass and tension, resulting in a higher pitched voice.

18. Question 18

    Q18. A scuba diver surfaces rapidly. What process occurs in their air-filled spaces, leading to a decrease in gas pressure?

    • A) Expansion due to increased temperature
    • B) Compression due to increased temperature
    • C) Expansion due to increased pressure
    • D) Compression due to decreased pressure

    Answer: Compression due to decreased pressure

    Explanation: Rapid ascent results in decreased ambient pressure, causing expansion of gases in air-filled spaces, not expansion due to temperature changes.

19. Question 19

    Q19. A group of people breathe in a mixture of gases, including CO2, which is absorbed into the bloodstream. What occurs to the pH of the arterial blood?

    • A) Increases due to acidic CO2
    • B) Decreases due to acidic CO2
    • C) Remains unchanged due to buffer system
    • D) Increases due to basic CO2

    Answer: Decreases due to acidic CO2

    Explanation: CO2 reacts with water to form carbonic acid, increasing the hydrogen ion concentration and decreasing pH.

20. Question 20

    Q20. A gas is added to a closed container, causing the pressure to increase. What is the effect on the temperature of the gas?

    • A) Increases due to increased pressure
    • B) Decreases due to increased pressure
    • C) Remains unchanged due to constant volume
    • D) Increases due to increased volume

    Answer: Increases due to increased pressure

    Explanation: According to Gay-Lussac's law, an increase in pressure at constant volume results in an increase in temperature.