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Which of the following statements about surface properties is/are correct? (A) Cloud is an emulsion-type colloid in which liquid is the dispersed phase and gas is the dispersion medium. (B) Adsorption is accompanied by a decrease in enthalpy and a decrease in entropy of the system. (C) Brownian motion of colloidal particles does not depend on the size of the particles but depends on the viscosity of the solution. (D) The critical temperatures of ethane and nitrogen are 563 K and 126 K, respectively. The adsorption of ethane will be more than that of nitrogen on the same amount of activated charcoal at a given temperature.

1. (A)
2. (B)
3. (C)
4. (D)

Correct answer: (D)

Solution

Statement B is correct: adsorption is exothermic (delta_H < 0) and decreases order on the surface compared to free gas, but the net effect is decrease in entropy. Statement D is correct: ethane (Tc = 563 K) is more easily liquefied than N2 (Tc = 126 K), meaning stronger van der Waals forces, so ethane adsorbs more on charcoal.

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