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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3ig218

Which of the following statements regarding molar mass determination of gases are correct?

  1. AMolar mass can be found from the mass of a known volume at known and using
  2. BFor a dissociating gas, the observed vapour density is lower than the value calculated from the formula
  3. CFor a gas that associates (dimerises), the observed molar mass is greater than the formula molar mass
  4. DGraham's law cannot be used to determine the molar mass of an unknown gas

Answer: A, B, C

gives (A). Dissociation raises the number of moles, lowering the average molar mass and vapour density (B). Association does the reverse (C). Comparing effusion rates with a reference gas is a standard way to get (D wrong).
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