July, 2022Flame Institute

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24. The respective speeds of the molecules are 1, 2, 3, 4 and 5 km/sec. The ratio of their r.m.s. velocity and the average velocity will be

(a) √11 :3 (b) 3:√11 (c) 1 : 2 …

22. The respective speeds of five molecules are 2, 1.5, 1.6, 1.6 and 1.2 km/sec. The most probable speed in km/sec will be

(a) 2 (b) 1.58 (c) 1.6 (d) 1.31 Answer-c (20)

19. The molecules of a given mass of a gas have a m.s. velocity of 200 m/sec at

27°C and 1.0×105 N/m2 pressure. When the temperature is 127°C and pressure is 0.5×105 N/m2 , the r.m.s. velocity in m/sec will be (a) (100√2)/3 …

20. Which of the following statement is true

(a) Absolute zero degree temperature is not zero energy temperature (b) Two different gases at the same temperature pressure have equal root mean square velocities (c) The root mean square speed of the molecules of different ideal gases, maintained at …

18. Speed of sound in a gas is v and r.m.s. velocity of the gas molecules is c. The ratio of v to c is

(a) 3/λ (b) λ/3 (c) √3/λ (d) √λ/3 Answer-d (6)

17. Moon has no atmosphere because

(a) The r.m.s. velocity of all gases is more than the escape velocity from moon’s surface (b) Its surface is not smooth (c) It is quite far away from the earth (d) It does not have population and plants Answer-a …

15. The temperature at which the root mean square velocity of a molecule will be doubled than at 100°C

(a) 1219°C (b) 1492°C (c) 400°C (d) 400 K Answer-a (12)

14. A gas is allowed to expand isothermally. The root mean square velocity of the molecules

(a) Will increase (b) Will decrease (c) Will remain unchanged (d) Depends on the other factors Answer-c (7)

13. A sample of gas is at 0°C. To what temperature it must be raised in order to double the r.m.s. speed of the molecule

(a) 270°C (b) 819°C (c) 1090°C (d) 100°C Answer-b (2)

12. The root mean square velocity of a gas molecule of mass m at a given temperature is proportional to

(a) m0 (b) m (c) √m …

83. An electron tube was sealed off during manufacture at a pressure of

1.2×10-7 mm of mercury at 27°C. Its volume is 100 cm3. The number of molecules that remain in the tube is (a) 2×1016 (b) 3×1015 (c) 3.86×1011 …

5. The r.m.s. velocity will be greater for

(a) Hydrogen (b) Oxygen (c) Equal for both (d) Nothing is definite Answer-a (8)

3. At a certain temperature, the m.s. velocity for

O2 is 400 m/sec. At the same temperature, the r.m.s. velocity for H2 molecules will be (a) 100 m/sec (b) 25 m/sec (c) 1600 m/sec (d) 6400 …

1. If the molecular weight of two gases are M1 and M1, then at a temperature the ratio of root mean square velocity v1 and v2 will be

(a) √M1/M2 (b) √M2/M1 (c) √(M1+M2)/(M1-M2 ) …

89. Air is pumped into an automobile tube upto a pressure of 200 kPa in the morning when the air temperature is 22°C. During the day, temperature rises to 42°C and the tube expands by 2%. The pressure of the air in the tube at this temperature, will be approximately

(a) 212 kPa (b) 209 kPa (c) 206 kPa (d) 200 kPa Answer-b (5)

88. Saturated vapour is compressed to half its volume without any change in temperature, then the pressure will be

(a) Doubled (b) Halved (c) The same (d) Zero Answer-c (6)

87. 125 ml of gas A at 0.60 atmosphere and 150 ml of gas B at 0.80 atmosphere pressure at same temperature is filled in a vessel of 1 litre volume. What will be the total pressure of mixture at the same temperature

(a) 0.140 atmosphere (b) 0.120 atmosphere (c) 0.195 atmosphere (d) 0.212 atmosphere Answer-c (77)

86. A gas is collected over the water at 25°C. The total pressure of moist gas was 735 mm of mercury. If the aqueous vapour pressure at 25°C is 23.8 mm. Then the pressure of dry gas is

(a) 760 mm (b) 758.8 mm (c) 710.8 mm (d) 711.2 mm Answer-d (25)

84. If the pressure of an ideal gas contained in a closed vessel is increased by 0.5%, the increase in temperature is 2K. The initial temperature of the gas is

(a) 27°C (b) 127°C (c) 300°C (d) 400°C Answer-b (10)

81. At 0°C the density of a fixed mass of a gas divided by pressure is x. At 100°C, the ratio will be

(a) x (b) (273/373)x (c) (373/273)x (d) (100/273)x Answer-b (3)

The gas in vessel is subjected to a pressure of 20 atmosphere at a temperature 27°C. The pressure of the gas in a vessel after one half of the gas is released from the vessel and the temperature of the remainder is raised by 50°C is

(a) 8.5 atm (b) 10.8 atm (c) 11.7 atm (d) 17 atm Answer-c (6)

78. The value of critical temperature in terms of Vander Waal’s constant a and b is

(a) Tc =(8a)/27Rb (b) Tc =(a)/2Rb (c) Tc =(8)/27Rb (d) Tc =(27a)/8Rb Answer-a (8)

11. For a gas, the r.m.s. speed at 800 K is

(a) Four times the value at 200 K (b) Half the value at 200 K (c) Twice the value at 200 K (d) Same as at 200 K Answer-c (12)

10. At what temperature is the root mean square velocity of gaseous hydrogen molecules is equal to that of oxygen molecules at 47°C

(a) 20 K (b) 80 K (c) – 73 K (d) 3 K Answer-a (3)

9. The root mean square velocity of the molecules in a sample of helium is 5/7th that of the molecules in a sample of hydrogen. If the temperature of hydrogen sample is 0°C, then the temperature of the helium sample is about

(a) 0°C (b) 0 K (c) 273°C (d) 100°C Answer-a (4)

8. The absolute temperature of a gas is determined by

(a) The average momentum of the molecules (b) The velocity of sound in the gas (c) The number of molecules in the gas (d) The mean square velocity of the molecules Answer-d (5)