In Langmuir’s model of adsorption of a gas on a solid surface

• A

  the rate of dissociation of adsorbed molecules from the surface does not depend on the surface covered
• B

  the adsorption at a single site on the surface may involve multiple molecules at the same time
• Correct answer
  C

  the mass of gas striking a given area of surface is proportional to the pressure of the gas
• D

  the mass of gas striking a given area of surface is independent of the pressure of the gas

Hence, the correct answer is option: 'C'.