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

1. The adsorption requires activation at 25ºC.
2. The adsorption is accompanied by a decrease in enthalpy.
3. The adsorption increases with increase of temperature.
4. The adsorption is irreversible.

Correct answer: The adsorption is accompanied by a decrease in enthalpy.

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