Answer:
(a) The low escape
speed (2.38 km/s) for the Moon is the reason that it has no atmosphere. Even
though the rms speed of the air molecules, which lies between 0.4 km/s to 0.8
km/s for its constituents (\[{{O}_{2}},\,{{N}_{2}},\,C{{O}_{2}}\] and water
vapours), is smaller than 2.38 km/s, a significant number of molecules have
speeds greater than 2.38 km/s and hence escape. When the rest of the molecules
arrange their speed distribution for equilibrium temperature, again there is a
significant number of molecules which have speeds greater than 2.38 km/s and
escape the have speed greater than 2.38 km/s and escape the Moon in the same
way as their predecessors. Due to this continual escape, the Moon has lost its
atmosphere.
(b) As the altitude
increases, the potential energy of air molecules increases and hence their K.E.
decrease. Since average K.E. of air molecules is directly proportional to the
temperature of the air. Therefore, temperature of the air decreases with
altitude.
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