The solution is as follows:
Answer 11:
Cold air is denser than hot air. Thus, when cold air from AC is given out, it moves downward causing cooling. If, AC is fitted downwards, then cold air won't rise and cooling effect will reduce.
Answer 12:
Expansion is increase in volume of the gas of fixed amount. This happens on the effect of heat. Heat increases the kinetic energy of the molecules that makes them move faster and increases momentary pressure, as a result of which gas expands.