From the following plots, find the correct option regarding
1
;
2
;
3
;
4
;
Official Solution
Correct Option: (4)
From PV and VT plots, higher temperature corresponds to higher volume at given pressure and vice versa. Analyze graph slopes accordingly.
02
PYQ 2022
medium
chemistryID: ap-eapce
Among the gases a, b, c, d, e, and f, the gases that show only positive deviation from ideal behavior at all pressures in the graph are:
1
b, c only
2
b, c, a only
3
d, e only
4
d, e, f only
Official Solution
Correct Option: (1)
Positive deviation from ideal behavior means compressibility factor at all pressures. From the graph, curves for b and c lie completely above the line , indicating that they show only positive deviation throughout.
03
PYQ 2022
medium
chemistryID: ap-eapce
Identify the correct variation of pressure and volume of a real gas (A) and an ideal gas (B) at constant temperature.
( )
1
2
3
4
Official Solution
Correct Option: (3)
For an ideal gas:
Real gases deviate from ideal behavior due to:
- Intermolecular forces
- Finite volume of molecules Hence:
- Real gas pressure is higher than ideal gas at the same volume, especially at high pressure or low temperature. Thus, real gas curve lies above the ideal gas curve on a vs. graph.
04
PYQ 2022
medium
chemistryID: ap-eapce
The standard molar enthalpy of vaporisation ( ) of A, B and C liquids is 23.3, 41 and 29 kJ mol respectively. The correct order of dipole-dipole attractive forces in these liquids is
1
B>C>A
2
B>A>C
3
A>C>B
4
A>B>C
Official Solution
Correct Option: (1)
The standard molar enthalpy of vaporization ( ) is the enthalpy change required to vaporize one mole of a liquid at its standard state (usually 1 bar pressure, specified temperature - often the normal boiling point).
A higher enthalpy of vaporization indicates that more energy is required to overcome the intermolecular attractive forces in the liquid state and convert the liquid into a gas.
Therefore, a higher generally implies stronger intermolecular forces. The question asks for the order of dipole-dipole attractive forces. While reflects the *total* strength of all types of intermolecular forces (London dispersion forces, dipole-dipole forces, hydrogen bonding), if we assume that dipole-dipole forces are a significant contributor and other factors are comparable or scale similarly, then a higher would suggest stronger dipole-dipole forces. This is a common simplifying assumption in such comparative questions unless other information (like molecular structure or polarity) is given. Given values:
Liquid A:
Liquid B:
Liquid C: Arranging these values in decreasing order:
(B)> (C)> (A). Since higher implies stronger intermolecular forces, the order of strength of these forces (and by inference, dipole-dipole forces if they are dominant or representative of the total) is:
B>C>A. This matches option (a).
05
PYQ 2022
medium
chemistryID: ap-eapce
The molecule which has more number of lone pair of electrons than the bond pair of electrons in its central atom is
1
XeF
2
ClF
3
XeF
4
SF
Official Solution
Correct Option: (1)
XeF has 2 bond pairs and 3 lone pairs on the central atom (Xe). Total 5 electron pairs form a trigonal bipyramidal arrangement. Since lone pairs are more than bond pairs on Xe, this satisfies the condition.
06
PYQ 2022
medium
chemistryID: ap-eapce
20 mL of gas A and 10 mL of gas B diffuses through a porous membrane separately in 1 minute. If the vapor density of B is X, what is the vapor density of A?
1
2x
2
4x
3
4
Official Solution
Correct Option: (3)
According to Graham's Law of Diffusion, the rate of diffusion ( ) of a gas is inversely proportional to the square root of its molar mass ( ) or its vapor density ( ), assuming constant temperature and pressure.
or (since Molar Mass ). Rate of diffusion ( ) can be expressed as Volume diffused ( ) per unit time ( ): .
Given:
For gas A: Volume mL, time minute.
Rate of diffusion of A: .
For gas B: Volume mL, time minute.
Rate of diffusion of B: . Let be the vapor density of gas A and be the vapor density of gas B.
From Graham's Law: . We are given . We need to find .
Substitute the rates of diffusion:
.
.
So, .
Square both sides:
.
.
Now, solve for :
. This matches option (c).
07
PYQ 2023
medium
chemistryID: ap-eapce
The isotopes of hydrogen are H, D and T. What is the approximate ratio of rate of diffusion of H , D , and T ?
1
0.4 : 0.5 : 0.7
2
0.7 : 0.5 : 0.4
3
0.5 : 0.25 : 0.167
4
0.167 : 0.25 : 0.5
Official Solution
Correct Option: (2)
According to Graham’s law of diffusion:
- Molar mass of H = 2
- Molar mass of D = 4 - Molar mass of T = 6 So:
Rounded to:
08
PYQ 2023
medium
chemistryID: ap-eapce
A gaseous mixture containing H , He, and O exerts a pressure of 1 bar. The weight percentage of H and He is 20 and 16 respectively. What is the ratio of partial pressures of O , He and H ?
1
1 : 2 : 5
2
5 : 2 : 1
3
2 : 1 : 5
4
2.5 : 1 : 1
Official Solution
Correct Option: (1)
Given:
- Weight % of H = 20%
- Weight % of He = 16%
- So, O = 100 - 20 - 16 = 64% Let’s convert to moles: Total moles = Partial pressure mole fraction: As the question asks for , the correct order is:
09
PYQ 2023
medium
chemistryID: ap-eapce
Elemental sulphur is known to exist as S (in vapor state) at 1000 K. At this temperature, if 1 g of sulphur occupies 2.62 L, its pressure (in atm) is (Assume S vapors follow the ideal gas equation. Given, R = 0.082 L atm mol K )
1
1.0
2
0.5
3
4.0
4
2.0
Official Solution
Correct Option: (2)
Use the ideal gas equation:
Given: K, L, g, g/mol
mol
atm
10
PYQ 2025
easy
chemistryID: ap-eapce
At T(K), a gaseous mixture contains H and O . The total pressure of the mixture is 2 bar. The weight percentage (w/w) of H is 33.33%. What is the approximate ratio of partial pressure of H and O ?
1
8 : 1
2
4 : 1
3
2 : 1
4
3 : 1
Official Solution
Correct Option: (1)
Step 1: Assume 100 g of mixture.
Given that H is 33.33% by weight, then:
Step 2: Convert masses to moles. Step 3: Use mole ratio to find partial pressure ratio.
Total moles = Step 4: Calculate the pressure ratio.
11
PYQ 2025
medium
chemistryID: ap-eapce
At 27 °C, rms velocity of SO is x ms and most probable velocity of O at 127 °C is y ms . The value of x : y is
1
3 : 4
2
4 : 3
3
2 : 3
4
3 : 2
Official Solution
Correct Option: (1)
Step 1: Recall the Formulas for RMS Velocity and Most Probable Velocity
The root mean square (rms) velocity ( ) is given by:
The most probable velocity ( ) is given by:
Where:
= Ideal gas constant
= Absolute temperature in Kelvin
= Molar mass of the gas in kg/mol Step 2: Convert Temperatures to Kelvin and Calculate Molar Masses
For SO :
Temperature
Molar mass of SO ( ): S = 32 g/mol, O = 16 g/mol.
For O :
Temperature
Molar mass of O ( ): O = 16 g/mol.
Step 3: Express x and y using the Velocity Formulas
Given is the rms velocity of SO :
Given is the most probable velocity of O :
Step 4: Calculate the Ratio x : y
Combine the square roots and cancel common terms ( and ):
Simplify the terms inside the square root:
Notice that is half of :
Simplify the fraction:
Therefore, the ratio is . Step 5: Analyze the Options
\begin{itemize} \item Option (1): 3 : 4. This matches our calculated ratio. \item Option (2): 4 : 3. Incorrect. \item Option (3): 2 : 3. Incorrect. \item Option (4): 3 : 2. Incorrect.
\end{itemize}
12
PYQ 2025
medium
chemistryID: ap-eapce
At the same pressure, the volume occupied by of gas "A" at is the same as of at . What is the molar mass (in ) of "A"? (Assume that gas "A" and are ideal gases) ( )
1
2
3
4
Official Solution
Correct Option: (2)
\textbf{Step 1: Recall the Ideal Gas Law} The ideal gas law is given by:
$ P V n R T n_1 T_1 n_2 T_2 \text{H}_2 m_A = 5.6 \, \text{g} M_A \text{H}_2 \text{H}_2 m_{\text{H}_2} = 1 \, \text{g} \text{H}_2 M_{\text{H}_2} = 2 \, \text{g mol}^{-1} \text{H}_2 \frac{n_1}{T_1} = \frac{n_2}{T_2} M_A 56 28 44 60 $ Incorrect — does not match the calculated value.
13
PYQ 2025
medium
chemistryID: ap-eapce
Consider the following: Statement I: Real gases exhibit ideal behaviour at high pressures and low temperatures. Statement II: At high pressure, all gases have compressibility factor (Z) either as 1 or< 1.
1
Both statement-I and statement-II are correct
2
Both statement-I and statement-II are not correct
3
Statement-I is correct, but statement-II is not correct
4
Statement-I is not correct, but statement-II is correct
Official Solution
Correct Option: (2)
- Statement I is incorrect: Real gases do **not** behave ideally at high pressure and low temperature — they deviate more significantly. - Statement II is incorrect: At high pressures, the compressibility factor can be greater than 1 (due to repulsive forces), not just ≤1.