Methylene blue adsorbs onto activated charcoal from its aqueous solution at 25°C in a process known as physical adsorption (physisorption).

(i) Physical adsorption of methylene blue on activated charcoal can occur at all temperatures, but it is more pronounced at lower temperatures. This means Option (A) is incorrect.

(ii) In the bulk, forces between molecules are balanced. However, molecules on the surface experience unbalanced or residual attractive forces, leading to higher surface energy. These unbalanced forces are responsible for van der Waals attractions between the adsorbent (activated charcoal) and the adsorbate (methylene blue). The formation of these weak attractions reduces the energy of surface molecules, resulting in a decrease in the system's enthalpy. Therefore, Option (B) is correct.

(iii) The extent of physisorption decreases as temperature increases because the weak van der Waals forces weaken at higher temperatures, reducing the adsorbate's ability to adhere to the adsorbent surface. Consequently, Option (C) is incorrect.

(iv) Physical adsorption is a reversible process. As the temperature decreases, the attractive forces between the adsorbent and adsorbate strengthen, increasing the extent of physisorption. Thus, Option (D) is incorrect.