(i) At the time of setting, the sun is at horizon. The light emitted by the sun has to travel a relatively longer distance through the atmosphere. As a result, blue part of light is scattered away by the particles in the atmosphere causing red part to be visible.
(ii)
Physical adsorption is an exothermic process. At equilibrium as the temperature is increased, kinetic energy of gas molecules increases with temperature.
(iii) Physical adsorption involves van der Waals forces, so any number of layers can be formed one over the other on the surface of the adsorbent. Chemical adsorption take place as a result of the reaction between adsorbent and absorbate. When the surface of adsorbent is covered with one layer, no further reaction can take place.