Which one of the following statements is not correct?

• A
  $A$. $A$ mixture of noble gases can be separated by adsorption on coconut charcoal at different temperatures.
• B
  $B$. Animal charcoal removes colours of impure coloured solutions by adsorption process.
• C
  $C$. Adsorption of reactants on the solid surface of the catalysts increases the rate of reaction.
• D
  $D$. Silica gel and alumina gel are used as adsorbents to increase moisture in air in the rooms.