Consider the following statements about Langmuir isotherm.
I. The free gas and adsorbed gas are in dynamic equilibrium.
II. All adsorption sites are equivalent.
III. The initially adsorbed layer can act as a substrate for further adsorption.
IV. The ability of a molecule to get adsorbed at a given site is independent of the occupation of neighboring sites.

The correct statements are

• A

  $\mathrm{I}, \mathrm{II}, \mathrm{III}$ and $\mathrm{IV}$
• Correct answer
  B

  $\mathrm{I}, \mathrm{II}$ and $\mathrm{IV}$
• C

  $\mathrm{I}, \mathrm{III},$ and $\mathrm{IV}$
• D

  $\mathrm{I}, \mathrm{II},$ and $\mathrm{III}$

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