I. fracC_PC_V=frac53$\frac{C_{P}}{C_{V}}=\frac{5}{3}$
B. Diatomic non-rigid gas
II. fracC_PC_V=frac75$\frac{C_{P}}{C_{V}}=\frac{7}{5}$
C. Monoatomic gas
III. fracC_PC_V=frac43$\frac{C_{P}}{C_{V}}=\frac{4}{3}$
D. Diatomic rigid gas
IV. fracC_PC_V=frac97$\frac{C_{P}}{C_{V}}=\frac{9}{7}$
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
Solution & Explanation
### Related Formula
The ratio of specific heats gamma$\gamma$ is related to degrees of freedom f$f$ by:
gamma = fracC_PC_V = 1 + frac2f$$\gamma = \frac{C_P}{C_V} = 1 + \frac{2}{f}$$
### Core Logic
Determine the degrees of freedom $
### Core Logic
Determine the degrees of freedom $f for each type of gas:
- **Monoatomic gas**: Translational only $ for each type of gas:
- **Monoatomic gas**: Translational only $\implies f = 3$
$gamma = 1 + frac23 = frac53 quad text(Matches C-I)$\gamma = 1 + \frac{2}{3} = \frac{5}{3} \quad \text{(Matches C-I)}$
- **Diatomic rigid gas**: Translational (3) + Rotational (2) $
- **Diatomic rigid gas**: Translational (3) + Rotational (2) $\implies f = 5$
$gamma = 1 + frac25 = frac75 quad text(Matches D-II)$\gamma = 1 + \frac{2}{5} = \frac{7}{5} \quad \text{(Matches D-II)}$
### Step 1: Check Remaining Categories
- **Diatomic non-rigid gas**: Translational (3) + Rotational (2) + Vibrational (2) $
### Step 1: Check Remaining Categories
- **Diatomic non-rigid gas**: Translational (3) + Rotational (2) + Vibrational (2) $\implies f = 7$
$gamma = 1 + frac27 = frac97 quad text(Matches B-IV)$\gamma = 1 + \frac{2}{7} = \frac{9}{7} \quad \text{(Matches B-IV)}$
- **Triatomic rigid gas**: Translational (3) + Rotational (3) $
- **Triatomic rigid gas**: Translational (3) + Rotational (3) $\implies f = 6$
$gamma = 1 + frac26 = 1 + frac13 = frac43 quad text(Matches A-III)$\gamma = 1 + \frac{2}{6} = 1 + \frac{1}{3} = \frac{4}{3} \quad \text{(Matches A-III)}$
This yields the matching order: A-III, B-IV, C-I, D-II.
### Pattern Recognition
Sees: Degrees of freedom and $
This yields the matching order: A-III, B-IV, C-I, D-II.
### Pattern Recognition
Sees: Degrees of freedom and $\gamma values.
Shortcut: Lower degrees of freedom result in higher $ values.
Shortcut: Lower degrees of freedom result in higher $\gamma values. Order of degrees of freedom: Monoatomic (3) < Diatomic rigid (5) < Triatomic rigid (6) < Diatomic non-rigid (7). Corresponding $ values. Order of degrees of freedom: Monoatomic (3) < Diatomic rigid (5) < Triatomic rigid (6) < Diatomic non-rigid (7). Corresponding $\gamma: $: $\frac{5}{3} > \frac{7}{5} > \frac{4}{3} > \frac{9}{7}$.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 11 Physics: Kinetic Theory
More Kinetic Theory Previous-Year Questions
Q30jee_main_2026_21_jan_eveningRMS Speed
The r.m.s speed of oxygen molecules at 47^circtextC$47^{\circ}\text{C}$ is equal to that of the hydrogen molecules kept at ________ ^circtextC$^{\circ}\text{C}$. (Mass of oxygen molecule / mass of hydrogen molecule = 32 / 2)
A.-235$-235$
B.-100$-100$
C.-253$-253$
D.-20$-20$
Solution
### Related Formula
V_textrms = sqrtfrac3RTM$$V_{\text{rms}} = \sqrt{\frac{3RT}{M}}$$
### Core Logic
Given that the RMS speed of oxygen molecules equals the RMS speed of hydrogen molecules:
V_textrms(O_2) = V_textrms(H_2)$$V_{\text{rms}(O_2)} = V_{\text{rms}(H_2)}$$sqrtfrac3RT_O_2M_O_2 = sqrtfrac3RT_H_2M_H_2$$\sqrt{\frac{3RT_{O_2}}{M_{O_2}}} = \sqrt{\frac{3RT_{H_2}}{M_{H_2}}}$$
Squaring both sides:
fracT_O_2M_O_2 = fracT_H_2M_H_2$$\frac{T_{O_2}}{M_{O_2}} = \frac{T_{H_2}}{M_{H_2}}$$
### Step 1: Absolute Temperature Conversion
Temperature of oxygen in Kelvin:
T_O_2 = 273 + 47 = 320 text K$$T_{O_2} = 273 + 47 = 320 \text{ K}$$
### Step 2: Evaluating for Hydrogen
Substitute the given mass ratio and absolute temperature:
frac32032 = fracT_H_22$$\frac{320}{32} = \frac{T_{H_2}}{2}$$10 = fracT_H_22$$10 = \frac{T_{H_2}}{2}$$T_H_2 = 20 text K$$T_{H_2} = 20 \text{ K}$$
### Step 3: Final Conclusion
Convert back to Celsius:
T_H_2 text in ^circtextC = 20 - 273 = -253^circtextC$$T_{H_2} \text{ in }^{\circ}\text{C} = 20 - 273 = -253^{\circ}\text{C}$$
### Pattern Recognition
Direct proportionality between Temperature and Molecular Mass for equal RMS speeds. T_1/M_1 = T_2/M_2$T_1/M_1 = T_2/M_2$. Always convert to Kelvin before evaluating.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 11 Physics: Kinetic Theory of Gases
Q37jee_main_2026_22_january_morningRotating Gas Cylinder Pressure
A cylindrical tube AB of length l, closed at both ends contains an ideal gas of 1 mol having molecular weight M. The tube is rotated in a horizontal plane with constant angular velocity omega$\omega$ about an axis perpendicular to AB and passing through the edge at end A, as shown in the figure. If P_A$P_{A}$ and P_B$P_{B}$ are the pressures at A and B respectively, then (Consider the temperature is same at all points in the tube)
Cylindrical tube rotating about an axis passing through end A.
### Related Formula
dP = rho omega^2 x dx, quad PM = rho RT$$dP = \rho \omega^2 x dx, \quad PM = \rho RT$$
### Core Logic
Cylindrical tube rotating about an axis passing through end A.
Setting up differential pressure equation:
A[(P+dP) - P] = (dm)(omega^2 x) implies dP = fracdmA omega^2 x$$A[(P+dP) - P] = (dm)(\omega^2 x) \implies dP = \frac{dm}{A} \omega^2 x$$
Substituting rho = fracPMRT$\rho = \frac{PM}{RT}$:
int_P_A^P_B fracdPP = fracomega^2 MRT int_0^l x dx$$\int_{P_A}^{P_B} \frac{dP}{P} = \frac{\omega^2 M}{RT} \int_0^l x dx$$lnleft(fracP_BP_Aright) = fracomega^2 l^2 M2RT implies P_B = P_A e^fracMomega^2 l^22RT$$\ln\left(\frac{P_B}{P_A}\right) = \frac{\omega^2 l^2 M}{2RT} \implies P_B = P_A e^{\frac{M\omega^2 l^2}{2RT}}$$
### Pattern Recognition
Sees: Rotating gas column with centrifugal pressure gradient.
Shortcut: Integrate hydrostatic equation with centripetal acceleration term.
Check: Matches option (1). ✓
### Chapter Mix
Class 11 Physics: Kinetic Theory of Gases
Q28jee_main_2026_22_january_eveningMean Free Path and Collision Frequency
Consider two boxes containing ideal gases A and B such that their temperatures, pressures and number densities are same. The molecular size of A is half of that of B and mass of molecule A is four times that of B. If the collision frequency in gas B is 32 times 10^18/mathrms$32 \times 10^{18}/\mathrm{s}$ then collision frequency in gas A is ____/s.
A.32 times 10^8$32 \times 10^{8}$
B.4 times 10^8$4 \times 10^{8}$
C.2 times 10^8$2 \times 10^{8}$
D.8 times 10^8$8 \times 10^{8}$
Solution
### Related Formula
Z = sqrt2pi d^2 N sqrtfrac8RTpi M$$Z = \sqrt{2}\pi d^{2} N \sqrt{\frac{8RT}{\pi M}}$$
where d$d$ is molecular diameter, N$N$ is number density, T$T$ is temperature, and M$M$ is molar mass.
### Core Logic
Given that T$T$ and N$N$ are identical for both gases:
Z propto fracd^2sqrtM$$Z \propto \frac{d^2}{\sqrt{M}}$$
From the problem statement:
d_A = fracd_B2, quad M_A = 4M_B$$d_A = \frac{d_B}{2}, \quad M_A = 4M_B$$
Calculating the ratio of collision frequencies:
fracZ_AZ_B = left(fracd_Ad_Bright)^2 times sqrtfracM_BM_A = left(frac12right)^2 times sqrtfrac14 = frac14 times frac12 = frac18$$\frac{Z_A}{Z_B} = \left(\frac{d_A}{d_B}\right)^2 \times \sqrt{\frac{M_B}{M_A}} = \left(\frac{1}{2}\right)^2 \times \sqrt{\frac{1}{4}} = \frac{1}{4} \times \frac{1}{2} = \frac{1}{8}$$
Substituting Z_B = 32 times 10^8 /mathrms$Z_B = 32 \times 10^8 /\mathrm{s}$:
Z_A = frac32 times 10^88 = 4 times 10^8 /mathrms$$Z_A = \frac{32 \times 10^8}{8} = 4 \times 10^8 /\mathrm{s}$$
### Step 1: Final Conclusion
The collision frequency in gas A is 4 times 10^8 /mathrms$4 \times 10^8 /\mathrm{s}$.
### Pattern Recognition
Proportionality check: Z propto d^2 / sqrtM$Z \propto d^2 / \sqrt{M}$.
Diameter halved implies 1/4$\implies 1/4$ factor. Mass quadrupled implies 1/sqrt4 = 1/2$\implies 1/\sqrt{4} = 1/2$ factor.
Combined factor = 1/4 times 1/2 = 1/8$= 1/4 \times 1/2 = 1/8$. 32 / 8 = 4$32 / 8 = 4$.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 11 Physics: Kinetic Theory of Gases
Q36jee_main_2026_23_january_eveningGas Laws
An air bubble of volume 2.9 \, mathrmcm^3$2.9 \, \mathrm{cm}^{3}$ rises from the bottom of a swimming pool of 5 m deep. At the bottom of the pool water temperature is 17 \, ^circmathrmC$17 \, ^{\circ}\mathrm{C}$ . The volume of the bubble when it reaches the surface, where the water temperature is 27 \, ^circmathrmC$27 \, ^{\circ}\mathrm{C}$ , is ____ mathrmcm^3$\mathrm{cm}^{3}$ .
(g = 10 \, mathrmm/s^2$g = 10 \, \mathrm{m/s}^{2}$ , density of water = 10^3 \, mathrmkg/m^3$10^{3} \, \mathrm{kg/m}^{3}$ , and 1 atm pressure is 10^5 \, mathrmPa$10^{5} \, \mathrm{Pa}$ )
A.4.2$4.2$
B.2.0$2.0$
C.3.0$3.0$
D.4.5$4.5$
Solution
### Related Formula
fracP_1 V_1T_1 = fracP_2 V_2T_2$$\frac{P_1 V_1}{T_1} = \frac{P_2 V_2}{T_2}$$P = P_textatm + rho g h$$P = P_{\text{atm}} + \rho g h$$
### Core Logic
Gas Laws diagram for Q36 - JEE Main 2026 Evening
For an air bubble rising in water, the number of moles of gas remains constant.
P_1$P_1$ = Pressure at bottom = P_textatm + rho gh$P_{\text{atm}} + \rho gh$T_1$T_1$ = Temperature at bottom = 17^circmathrmC = 290 \, mathrmK$17^{\circ}\mathrm{C} = 290 \, \mathrm{K}$V_1$V_1$ = 2.9 \, mathrmcm^3$2.9 \, \mathrm{cm}^3$P_2$P_2$ = Pressure at surface = P_textatm$P_{\text{atm}}$T_2$T_2$ = Temperature at surface = 27^circmathrmC = 300 \, mathrmK$27^{\circ}\mathrm{C} = 300 \, \mathrm{K}$
### Step 1: Calculate Pressures
P_1 = 10^5 + (10^3 times 10 times 5) = 10^5 + 50,000 = 1.5 times 10^5 \, mathrmPa$$P_1 = 10^5 + (10^3 \times 10 \times 5) = 10^5 + 50,000 = 1.5 \times 10^5 \, \mathrm{Pa}$$P_2 = 10^5 \, mathrmPa$$P_2 = 10^5 \, \mathrm{Pa}$$
### Step 2: Apply Ideal Gas Law
frac(1.5 times 10^5)(2.9)290 = frac(10^5)(V_2)300$$\frac{(1.5 \times 10^5)(2.9)}{290} = \frac{(10^5)(V_2)}{300}$$frac1.5 times 2.9290 = fracV_2300$$\frac{1.5 \times 2.9}{290} = \frac{V_2}{300}$$V_2 = frac1.5 times 2.9 times 300290 = 1.5 times 3 = 4.5 \, mathrmcm^3$$V_2 = \frac{1.5 \times 2.9 \times 300}{290} = 1.5 \times 3 = 4.5 \, \mathrm{cm}^3$$
### Pattern Recognition
Standard combined gas law application. Always remember to convert Celsius to Kelvin and carefully compute gauge pressure plus atmospheric pressure for the submerged state.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 11 Physics: Kinetic Theory of Gases
Class 11 Physics: Mechanical Properties of Fluids
Q47jee_main_2026_24_january_morningIdeal Gas Laws
A gas of certain mass filled in a closed cylinder at a pressure of 3.23 kPa has temperature 50^circtextC$50^{\circ}\text{C}$. The gas is now heated to double its temperature. The modified pressure is ____ Pa.
Numerical Answer.Answer: 3730 to 3730
Solution
### Related Formula
P propto T quad (textGay-Lussac's Law for constant V)$$P \propto T \quad (\text{Gay-Lussac's Law for constant V})$$
### Core Logic
Since the gas is filled in a closed cylinder, the volume V$V$ remains constant.
Therefore, P propto T$P \propto T$ (where T must be in Kelvin).
Initial temperature T_i = 50^circtextC = 273 + 50 = 323 text K$T_i = 50^{\circ}\text{C} = 273 + 50 = 323 \text{ K}$.
Final temperature T_f = 100^circtextC = 273 + 100 = 373 text K$T_f = 100^{\circ}\text{C} = 273 + 100 = 373 \text{ K}$.
Note: The phrasing "double its temperature" is slightly ambiguous (Celsius vs Kelvin). As per standard interpretations in such exams, "double its temperature" given in Celsius means 100^circtextC$100^{\circ}\text{C}$ (which is 373 K). If it meant doubling absolute temperature, final would be 646 K. The official interpretation used here doubles the Celsius scale value.
### Step 1: Calculate Final Pressure
Using the relation:
fracP_fP_i = fracT_fT_i$$\frac{P_f}{P_i} = \frac{T_f}{T_i}$$fracP_f3.23 times 10^3 = frac373323$$\frac{P_f}{3.23 \times 10^3} = \frac{373}{323}$$P_f = 3.23 times 10^3 times frac373323 = 3.73 times 10^3 text Pa$$P_f = 3.23 \times 10^3 \times \frac{373}{323} = 3.73 \times 10^3 \text{ Pa}$$P_f = 3730 text Pa$$P_f = 3730 \text{ Pa}$$
### Pattern Recognition
Be highly alert to 'double temperature' traps when given in Celsius. The question specifically intends 50^circ rightarrow 100^circ$50^\circ \rightarrow 100^\circ$, not 323textK rightarrow 646textK$323\text{K} \rightarrow 646\text{K}$. Calculating with 373K nicely cancels with the 3.23textkPa$3.23\text{kPa}$.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 11 Physics: Kinetic Theory
Class 11 Physics: Thermodynamics
More Kinetic Theory Questions — jee_main_2025_07_april_morning
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