Methylene blue, from its aqueous solution, is adsorbed on activated charcoal at 25o C . For this process the correct statement is

Physical adsorption takes place with decrease in enthalpy, thus exothermic change. It is physical adsorption and does not require activation. Thus, (a) is incorrect. Being physical adsorption ΔH<0 thus, (b) is correct. Exothermic reaction if favoured a low temperature thus (c) is incorrect. Physical adsorption is always reversible, thus (d) is incorrect.