JEE Main Previous Year Questions (2025): Gaseous State

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JEE Main Previous Year Questions 
(2025): Gaseous State 
Q1: At the sea level, the dry air mass percentage composition is given as nitrogen gas: 70.0 , 
oxygen gas: 27.0 and argon gas: 3.0 . If total pressure is 1.15 atm , then calculate the ratio of 
following respectively: 
(i) partial pressure of nitrogen gas to partial pressure of oxygen gas 
(ii) partial pressure of oxygen gas to partial pressure of argon gas 
(Given: Molar mass of ?? , ?? and Ar are 14,16 and ???? ?? ?????? -?? respectively.) 
JEE Main 2025 (Online) 7th April Morning Shift 
A. 5.46, 17.8 
B. 2.96, 11.2 
C. 4.26, 19.3 
D. 2.59, 11.85 
Ans: A 
Solution: 
Partial Pressure Ratio of Nitrogen to Oxygen : 
The partial pressure of a gas is calculated using its mole fraction. The mole fraction is the ratio of the 
number of moles of the gas to the total number of moles of all gases. 
For nitrogen ( N
2
 ), the mole fraction 
?? N
2
?? N
2
+?? 0
 
2
+?? Ar
 can be simplified as 
70/28
70/28+27/32+3/40
. 
For oxygen ( O
2
 ), the mole fraction is 
27/32
70/28+27/32+3/40
. 
Therefore, the ratio of the partial pressure of nitrogen to oxygen is : 
?? N
2
?? O
2
=
 mole fraction of 
 mole fraction of 
 
N
2
O
2
=
70/28
27/32
= ?? . ???? 
Partial Pressure Ratio of Oxygen to Argon : 
For argon (Ar), the mole fraction is 
3/40
70/28+27/32+3/40
. 
The ratio of the partial pressure of oxygen to argon is : 
P
O
2
P
Ar
=
 mole fraction of 
 mole fraction of 
 O
2
=
27/32
3/40
= ???? . ????