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NEET Chemistry MCQ
Quiz 1
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Q.1
The value of gas constant per degree per mole is approximately
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1 Cal
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2 cal
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3 cal
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4 cal
Explanation
The gas constant R ≈ 1.987 cal/(mol·K), commonly rounded to about 2 cal per degree per mole.
Q.2
Vander Waal's constants 'a' and 'b' are related with _______ respectively
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Attractive force and bond energy of molecules
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Volume and repulsive force of molecules
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Shape and repulsive forces of molecules
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Attractive force and volume of the molecules
Explanation
In the van der Waals equation, the constant 'a' corrects for the attractive intermolecular forces between gas molecules (which reduce the pressure below the ideal value), while the constant 'b' corrects for the finite volume actually occupied by the gas molecules themselves (the volume unavailable for free molecular motion).
Q.3
A gas described by van der Waals equation (A) behaves similar to an ideal gas in the limit of large molar volumes (B) behaves similar to an ideal gas in the limit of large pressures (C) is characterized by van der Waals coefficients that are dependent on the identity of the gas but are independent of the temperature. (D) has the pressure that is lower than the pressure exerted by the same gas behaving ideally. Choose the correct option from below :
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(A) and (B) are correct
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(A) and (C) are correct
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(A), (B) and (D) are correct
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(A) ,(C) and (D) are correct
Explanation
Solution: checking each statement. (A) True — at large molar volumes, the correction terms a/V² and b become negligible compared to the volume itself, so the gas behaves essentially ideally. (B) False — at high pressure molecules are pushed close together, making both the finite-volume and intermolecular-attraction corrections MORE significant, not less — real gases deviate FURTHER from ideal behaviour at high pressure. (C) True — the van der Waals constants a and b are specific to each gas (depending on its molecular size and intermolecular forces) but do not themselves change with temperature. (D) True — attractive intermolecular forces pull molecules inward, reducing the pressure they actually exert compared to what an ideal gas would exert under the same conditions — this is exactly why the vdW equation adds a correction term (a/V²) back onto the observed pressure. So (A), (C) and (D) are correct; (B) is false.
Q.4
How does the surface tension of a liquid vary with increase in temperature?
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Remains same
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Decreases
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Increases
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No regular pattern is followed
Explanation
Surface tension arises from intermolecular attractive forces at a liquid's surface. As temperature rises, molecules gain kinetic energy and these attractive forces weaken, so surface tension decreases with increasing temperature.
Q.5
The rate of diffusion of methane at a given temperature is twice of a gas X. The molecular weight of X is
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64
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16
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32
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8
Explanation
By Graham's law of diffusion, rate ∝ 1/√M (M = molar mass). Given rate(CH₄) = 2 × rate(X): 2 = √(M_X / M_CH₄) = √(M_X / 16) Squaring: 4 = M_X / 16 → M_X = 64.
Q.6
Match the column
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p -> i , q-> iii, r -> ii, s -> iv
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p -> iv , q-> iii, r -> ii, s -> i
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p -> iv , q-> iii, r -> i, s -> ii
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p -> iii , q-> iv, r -> ii, s -> i
Explanation
Matching each law to its expression: (p) Boyle's Law: P ∝ 1/V (constant n, T) → (iii) (q) Charles' Law: V ∝ T (constant n, P) → (iv) (r) Dalton's Law: P_total = P₁ + P₂ + P₃ + ... (constant T, V) → (ii) (s) Graham's Law: rate ∝ 1/√M → (i) So: p → iii, q → iv, r → ii, s → i.
Q.7
What is SI unit of viscosity coefficient (η)?
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Pascal
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Ns m–2
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km–2 s
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N m–2
Explanation
The SI unit of dynamic viscosity (η) is the pascal-second (Pa·s), which is dimensionally the same as N·s/m² — force multiplied by time, divided by area. "Pascal" alone (N/m²) is a unit of pressure, missing the time factor that viscosity requires.
Q.8
Which of the following gases will have the highest rate of diffusion?
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O2
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C O2
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NH3
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N2
Explanation
By Graham's law, lighter gases diffuse faster (rate ∝ 1/√M). Among O₂ (32), CO₂ (44), NH₃ (17) and N₂ (28), NH₃ has the lowest molar mass, so it diffuses fastest.
Q.9
In Van der waals equation of state for a non-ideal gas, the term that accounts for intermolecular forces is
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(V-b)
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RT
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$P + \frac {a}{V^2}
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1/RT
Explanation
In the van der Waals equation, (P + a/V²) is the pressure-correction term — it accounts for the fact that intermolecular attractive forces reduce the pressure a real gas actually exerts compared to an ideal gas, so 'a/V²' is added back to compensate. ((V − b) instead corrects for the finite volume occupied by the gas molecules themselves.)
Q.10
Which of the following gas molecules has the largest mean free path?
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O2
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N2
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H2
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Cl2
Explanation
Mean free path (the average distance a molecule travels between collisions) tends to be larger for smaller, lighter molecules, which have a smaller effective collision cross-section. Among O₂, N₂, H₂ and Cl₂, H₂ is the smallest molecule, giving it the largest mean free path.
Q.11
A person living in Nainital observed that cooking food without using pressure cooker takes more time. The reason for this observation is that at high altitude:
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pressure increases
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temperature decreases
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pressure decreases
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) temperature increases
Explanation
Atmospheric pressure decreases with increasing altitude. Since a liquid boils when its vapour pressure equals the surrounding atmospheric pressure, lower pressure at high altitude (like Nainital) means water boils at a lower temperature — so food, cooked at a lower boiling point without the higher pressure a pressure cooker provides, takes longer to cook.
Q.12
Temperature which is same in both Celsius scale and Fahrenheit scale:
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0°C
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32°F
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-40°C
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40°C
Explanation
Using F = (9/5)C + 32 and setting F = C: C = (9/5)C + 32 → −(4/5)C = 32 → C = −40. So −40°C and −40°F are numerically the same temperature — the one point where both scales agree.
Q.13
Behavior of real gases near to that of ideal gases if:
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Low pressure and low temperature
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High Pressure and low temperature
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Low pressure and high temperature
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High Pressure and high temperature
Explanation
Real gases behave most like ideal gases at low pressure (molecules are far apart, so their own volume and mutual attractions barely matter) and high temperature (molecules have enough kinetic energy that weak intermolecular attractions become negligible).
Q.14
Compressibility factor for ideal gas is
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0
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lies between 0 and 1
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1
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Greater than 1
Explanation
The compressibility factor Z = PV/(nRT). For an ideal gas, PV = nRT exactly by definition, so Z = 1 always.
Q.15
One gram molecule of a gas at N.T.P. occupies 22.4 litres.? This fact was derived from
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Dalton's theory
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Avogadro's hypothesis
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Grahm's law
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Law of gaseous volume
Explanation
The fact that one gram-molecule (one mole) of any gas occupies 22.4 litres at NTP follows from Avogadro's hypothesis — equal volumes of different gases, at the same temperature and pressure, contain equal numbers of molecules, so a fixed number of molecules (one mole) always occupies the same volume under given conditions.
Q.16
In the ideal gas equation, the gas constant R has the dimensions
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mole-atm K-1
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erg K-1
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litre-atm K-1 mole-1
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litre mole
Explanation
From PV = nRT, rearranged R = PV/(nT): pressure × volume, divided by (amount × temperature), giving R the units litre·atm·K⁻¹·mol⁻¹ (when P is in atmospheres and V in litres).
Q.17
Rate of diffusion of a gas is
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Directly proportional to its density
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Directly proportional to its molecular mass
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Directly proportional to the square root of its molecular mass
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Inversely proportional to the square root of its molecular mass
Explanation
Graham's law of diffusion states that the rate of diffusion of a gas is inversely proportional to the square root of its molecular mass — lighter gas molecules diffuse faster.
Q.18
Assertion (A): The temperature at which vapour pressure of a liquid is equal to the external pressure is called boiling temperature. Reason (R) : At high altitude atmospheric pressure is high.
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Both A and R are true and R is the correct explanation of A
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Both A and R are true but R is not the correct explanation of A.
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A is true but R is false.
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A is false but R is true.
Explanation
The Assertion is a correct, standard definition of boiling temperature. But the Reason is false: atmospheric pressure actually DECREASES with altitude, not increases — which is precisely why water boils at a lower temperature on a mountain or hill station (as in the earlier Nainital example), not a higher one.
Q.19
Which one of the following is not a unit of pressure
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Kg m/s2
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Torr
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Pascal
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Bar
Explanation
kg·m/s² is the dimensional combination for force (this is exactly the newton, kg·m/s²) — not pressure, which requires force divided by area (N/m²). Torr, Pascal and Bar are all genuine, standard units of pressure.
Q.20
A real gas most closely approaches the behavior of an ideal gas at
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16 atm and 200 K
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1 atm and 273 K
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15 atm and 600 K
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0.1 atm and 400 K
Explanation
Real-gas behaviour approaches ideal-gas behaviour best under low pressure and high temperature. Among the given conditions, 0.1 atm (the lowest pressure by far) combined with 400 K (a relatively high temperature) is the combination closest to ideal-gas conditions.
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