Consider the General Gas-Phase Reaction of a Molecular Substance, A

Consider the general gas-phase reaction of a molecular substance, A:
1. At very low pressures many such reactions occur by the following mechanism:
2. 3. (A* represents a molecule with sufficient energy to overcome the activation energy barrier.)
A) Which of the three reactions above is/are elementary?
B) Where appropriate, identify the molecularity of the reactions.
C) Show that the proposed mechanism is consistent with reaction 1, the observed reaction.
D) Given the mechanism above, suggest a likely rate law for reaction (1).