Question:

Consider the following table :
Gas\(a/(\mathrm{kPa\ dm^6\ mol^{-1}})\)\(b/(\mathrm{dm^3\ mol^{-1}})\)
A642.320.05196
B155.210.04136
C431.910.05196
D155.210.4382
\(a\) and \(b\) are van der Waals constants. The correct statement about the gases is :

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A larger \(a\) means stronger attraction (smaller volume); a larger \(b\) means more repulsion (higher Z, less compressible).
Updated On: Nov 5, 2026
  • Gas C will occupy more volume than gas A; gas B will be more compressible than gas D
  • Gas C will occupy lesser volume than gas A; gas B will be more compressible than gas D
  • Gas C will occupy lesser volume than gas A; gas B will be lesser compressible than gas D
  • Gas C will occupy more volume than gas A; gas B will be lesser compressible than gas D
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The Correct Option is A

Solution and Explanation

Gas A and gas C have the same \(b\) (0.05196), but \(a_A = 642.32 > a_C = 431.91\). A larger \(a\) means stronger intermolecular attraction, which pulls the molecules closer and reduces the volume at a given \(P\) and \(T\) (from \(V \approx \frac{RT}{P} + b - \frac{a}{RT}\)). So gas A occupies less volume, and gas C occupies more volume than gas A.
Gas B and gas D have the same \(a\) (155.21), but \(b_B = 0.04136 < b_D = 0.4382\). A larger \(b\) means a larger repulsive (excluded-volume) contribution, so \(Z = \frac{PV}{RT}\) is greater and the gas is harder to compress. So gas D is less compressible and gas B is more compressible than gas D.
Hence: gas C occupies more volume than A; B is more compressible than D.
Answer: (1) Gas C will occupy more volume than gas A; gas B will be more compressible than gas D
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