JEE Main Previous Year Questions (2025): Kinetic Theory of Gases

 Page 1


JEE Main Previous Year Questions 
(2025): Kinetic Theory of Gases 
Q1. For a particular ideal gas which of the following graphs represents the variation of 
mean squared velocity of the gas molecules with temperature? 
A.  
B.  
C.  
D.  
Ans: B 
Solution: 
Page 2


JEE Main Previous Year Questions 
(2025): Kinetic Theory of Gases 
Q1. For a particular ideal gas which of the following graphs represents the variation of 
mean squared velocity of the gas molecules with temperature? 
A.  
B.  
C.  
D.  
Ans: B 
Solution: 
V
ms
=
v
3????
M
 
V
rms
2
= 3RT/M 
Hence we can conclude that V
rms
2
 is directly proportional to temperature 
y = mx 
? Graph will be straight line 
Q2. The ratio of vapour densities of two gases at the same temperature is 
?? ????
, then the 
ratio of r.m.s. velocities will be: 
A. 
25
4
 
B. 
2
5
 
C. 
5
2
 
D. 
4
25
 
Ans: C 
Solution: 
( Vapor density ) = (
 Molar mass 
2
), I.e, ???? =
?? 2
 
?? rms
=
v
3????
?? ?? 2
?? 1
= v
?? 1
?? 2
=
v
25
4
=
5
2
 
 
Q3. The kinetic energy of translation of the molecules in 50 g of ????
?? gas at ????
°
?? is 
A. 4205.5 J 
B. 4102.8 J 
C. 3582.7 J 
D. 3986.3 J 
Ans: B 
Solution: 
Kinetic energy of translation =
3
2
?????? 
?? =
50 g
44 g
=
25
22
 mol
?? = 17
°
C = 290 K
 
Page 3


JEE Main Previous Year Questions 
(2025): Kinetic Theory of Gases 
Q1. For a particular ideal gas which of the following graphs represents the variation of 
mean squared velocity of the gas molecules with temperature? 
A.  
B.  
C.  
D.  
Ans: B 
Solution: 
V
ms
=
v
3????
M
 
V
rms
2
= 3RT/M 
Hence we can conclude that V
rms
2
 is directly proportional to temperature 
y = mx 
? Graph will be straight line 
Q2. The ratio of vapour densities of two gases at the same temperature is 
?? ????
, then the 
ratio of r.m.s. velocities will be: 
A. 
25
4
 
B. 
2
5
 
C. 
5
2
 
D. 
4
25
 
Ans: C 
Solution: 
( Vapor density ) = (
 Molar mass 
2
), I.e, ???? =
?? 2
 
?? rms
=
v
3????
?? ?? 2
?? 1
= v
?? 1
?? 2
=
v
25
4
=
5
2
 
 
Q3. The kinetic energy of translation of the molecules in 50 g of ????
?? gas at ????
°
?? is 
A. 4205.5 J 
B. 4102.8 J 
C. 3582.7 J 
D. 3986.3 J 
Ans: B 
Solution: 
Kinetic energy of translation =
3
2
?????? 
?? =
50 g
44 g
=
25
22
 mol
?? = 17
°
C = 290 K
 
? Kinetic energy of translation 
 =
3
2
(
25
22
) (8.3)(290)J
 = 4102.8 J
 
 
Q4: The mean free path and the average speed of oxygen molecules at 300 K and 1 
atm are ?? × ????
-?? ?? and ?????? ?? /?? respectively. Find the frequency of its collisions. 
A. 2 × 10
10
/s 
B. 9 × 10
5
/s 
C. 2 × 10
9
/s 
D. 5 × 10
8
/s 
Ans: C 
Solution: 
Frequency =
1
?? =
?? avg 
?? 
 
=
600
3 × 157
= 2 × 10
9
sec
-1
 
 
Q5: The helium and argon are put in the flask at the same room temperature ( 300 K ). 
The ratio of average kinetic energies (per molecule) of helium and argon is : 
(Give : Molar mass of helium = ?? ?? /?????? , Molar mass of argon = ???? ?? /?????? ) 
A. 1 : 10 
B. 10: 1 
C. 1: v 10 
D. 1: 1 
Ans: D 
Solution: 
?? · ?? =
?? 2
?? ?? 
For He and Arf = 3 
K · E
Be
 K · E
Ar
=
1
1
 
 
Q6: ?? ?? is the specific heat ratio of monoatomic gas A having 3 translational degrees of 
freedom. ?? ?? is the specific heat ratio of polyatomic gas ?? having 3 translational, 3 
Page 4


JEE Main Previous Year Questions 
(2025): Kinetic Theory of Gases 
Q1. For a particular ideal gas which of the following graphs represents the variation of 
mean squared velocity of the gas molecules with temperature? 
A.  
B.  
C.  
D.  
Ans: B 
Solution: 
V
ms
=
v
3????
M
 
V
rms
2
= 3RT/M 
Hence we can conclude that V
rms
2
 is directly proportional to temperature 
y = mx 
? Graph will be straight line 
Q2. The ratio of vapour densities of two gases at the same temperature is 
?? ????
, then the 
ratio of r.m.s. velocities will be: 
A. 
25
4
 
B. 
2
5
 
C. 
5
2
 
D. 
4
25
 
Ans: C 
Solution: 
( Vapor density ) = (
 Molar mass 
2
), I.e, ???? =
?? 2
 
?? rms
=
v
3????
?? ?? 2
?? 1
= v
?? 1
?? 2
=
v
25
4
=
5
2
 
 
Q3. The kinetic energy of translation of the molecules in 50 g of ????
?? gas at ????
°
?? is 
A. 4205.5 J 
B. 4102.8 J 
C. 3582.7 J 
D. 3986.3 J 
Ans: B 
Solution: 
Kinetic energy of translation =
3
2
?????? 
?? =
50 g
44 g
=
25
22
 mol
?? = 17
°
C = 290 K
 
? Kinetic energy of translation 
 =
3
2
(
25
22
) (8.3)(290)J
 = 4102.8 J
 
 
Q4: The mean free path and the average speed of oxygen molecules at 300 K and 1 
atm are ?? × ????
-?? ?? and ?????? ?? /?? respectively. Find the frequency of its collisions. 
A. 2 × 10
10
/s 
B. 9 × 10
5
/s 
C. 2 × 10
9
/s 
D. 5 × 10
8
/s 
Ans: C 
Solution: 
Frequency =
1
?? =
?? avg 
?? 
 
=
600
3 × 157
= 2 × 10
9
sec
-1
 
 
Q5: The helium and argon are put in the flask at the same room temperature ( 300 K ). 
The ratio of average kinetic energies (per molecule) of helium and argon is : 
(Give : Molar mass of helium = ?? ?? /?????? , Molar mass of argon = ???? ?? /?????? ) 
A. 1 : 10 
B. 10: 1 
C. 1: v 10 
D. 1: 1 
Ans: D 
Solution: 
?? · ?? =
?? 2
?? ?? 
For He and Arf = 3 
K · E
Be
 K · E
Ar
=
1
1
 
 
Q6: ?? ?? is the specific heat ratio of monoatomic gas A having 3 translational degrees of 
freedom. ?? ?? is the specific heat ratio of polyatomic gas ?? having 3 translational, 3 
rotational degrees of freedom and 1 vibrational mode. If 
?? ?? ?? ?? = (?? +
?? ?? ), then the value 
of ?? is ____ . 
Ans: 3 
Solution: 
?? ?? ?? ?? =
f
A
+ 2
f
A
×
f
B
f
B
+ 2
 =
3 + 2
3
×
(6 + 2)
(6 + 2) + 2
 =
5
3
×
8
10
=
40
30
 ?
40
30
= 1 +
1
n
 ?
40
30
- 1 =
1
n
 ? n = 3
 
 
Q7: Match the List - I with List - II 
 List-I  List-II 
A. Triatomic rigid gas I. 
?? ?? ?? ?? =
?? ?? 
B. Diatomic non-rigid gas II. 
?? ?? ?? ?? =
?? ?? 
C. Monoatomic gas III. 
?? ?? ?? ?? =
?? ?? 
D. Diatomic rigid gas IV 
?? ?? ?? ?? =
?? ?? 
Choose the correct answer from the options given below : 
A. A-III, B-IV, C-I, D-II 
B. A-III, B-II, C-IV, D-I 
C. A-II, B-IV, C-I, D-III 
D. A-IV, B-II, C-III, D-I 
Ans: A 
Solution: 
?? = 1 +
2
f
 
?? = 6, Triatomic rigid gas 
f = 7, Diatomic non-rigid gas 
?? = 5, Diatomic rigid gas 
Page 5


JEE Main Previous Year Questions 
(2025): Kinetic Theory of Gases 
Q1. For a particular ideal gas which of the following graphs represents the variation of 
mean squared velocity of the gas molecules with temperature? 
A.  
B.  
C.  
D.  
Ans: B 
Solution: 
V
ms
=
v
3????
M
 
V
rms
2
= 3RT/M 
Hence we can conclude that V
rms
2
 is directly proportional to temperature 
y = mx 
? Graph will be straight line 
Q2. The ratio of vapour densities of two gases at the same temperature is 
?? ????
, then the 
ratio of r.m.s. velocities will be: 
A. 
25
4
 
B. 
2
5
 
C. 
5
2
 
D. 
4
25
 
Ans: C 
Solution: 
( Vapor density ) = (
 Molar mass 
2
), I.e, ???? =
?? 2
 
?? rms
=
v
3????
?? ?? 2
?? 1
= v
?? 1
?? 2
=
v
25
4
=
5
2
 
 
Q3. The kinetic energy of translation of the molecules in 50 g of ????
?? gas at ????
°
?? is 
A. 4205.5 J 
B. 4102.8 J 
C. 3582.7 J 
D. 3986.3 J 
Ans: B 
Solution: 
Kinetic energy of translation =
3
2
?????? 
?? =
50 g
44 g
=
25
22
 mol
?? = 17
°
C = 290 K
 
? Kinetic energy of translation 
 =
3
2
(
25
22
) (8.3)(290)J
 = 4102.8 J
 
 
Q4: The mean free path and the average speed of oxygen molecules at 300 K and 1 
atm are ?? × ????
-?? ?? and ?????? ?? /?? respectively. Find the frequency of its collisions. 
A. 2 × 10
10
/s 
B. 9 × 10
5
/s 
C. 2 × 10
9
/s 
D. 5 × 10
8
/s 
Ans: C 
Solution: 
Frequency =
1
?? =
?? avg 
?? 
 
=
600
3 × 157
= 2 × 10
9
sec
-1
 
 
Q5: The helium and argon are put in the flask at the same room temperature ( 300 K ). 
The ratio of average kinetic energies (per molecule) of helium and argon is : 
(Give : Molar mass of helium = ?? ?? /?????? , Molar mass of argon = ???? ?? /?????? ) 
A. 1 : 10 
B. 10: 1 
C. 1: v 10 
D. 1: 1 
Ans: D 
Solution: 
?? · ?? =
?? 2
?? ?? 
For He and Arf = 3 
K · E
Be
 K · E
Ar
=
1
1
 
 
Q6: ?? ?? is the specific heat ratio of monoatomic gas A having 3 translational degrees of 
freedom. ?? ?? is the specific heat ratio of polyatomic gas ?? having 3 translational, 3 
rotational degrees of freedom and 1 vibrational mode. If 
?? ?? ?? ?? = (?? +
?? ?? ), then the value 
of ?? is ____ . 
Ans: 3 
Solution: 
?? ?? ?? ?? =
f
A
+ 2
f
A
×
f
B
f
B
+ 2
 =
3 + 2
3
×
(6 + 2)
(6 + 2) + 2
 =
5
3
×
8
10
=
40
30
 ?
40
30
= 1 +
1
n
 ?
40
30
- 1 =
1
n
 ? n = 3
 
 
Q7: Match the List - I with List - II 
 List-I  List-II 
A. Triatomic rigid gas I. 
?? ?? ?? ?? =
?? ?? 
B. Diatomic non-rigid gas II. 
?? ?? ?? ?? =
?? ?? 
C. Monoatomic gas III. 
?? ?? ?? ?? =
?? ?? 
D. Diatomic rigid gas IV 
?? ?? ?? ?? =
?? ?? 
Choose the correct answer from the options given below : 
A. A-III, B-IV, C-I, D-II 
B. A-III, B-II, C-IV, D-I 
C. A-II, B-IV, C-I, D-III 
D. A-IV, B-II, C-III, D-I 
Ans: A 
Solution: 
?? = 1 +
2
f
 
?? = 6, Triatomic rigid gas 
f = 7, Diatomic non-rigid gas 
?? = 5, Diatomic rigid gas 
f = 3, monoatomic rigid gas 
?? = 1 +
2
6
=
4
3
 (Triatomic) 
?? = 1 +
2
7
=
9
7
 (Diatomic, non-rigid) 
?? = 1 +
2
5
=
7
5
 (Diatomic, rigid) 
?? = 1 +
2
3
=
5
3
( Monoatomic, rigid) 
A-III, B-IV, C-I, D-II