Answer to Question 1
mAs
Rationale: Milliamperage-seconds, mAs, contributes to the overall blackness of the image. It represents the quantity of radiation produced.
Answer to Question 2
the arm closest to the image receptor
Rationale: The arm closest to the IR should be elevated and the opposite shoulder/arm stretched down. If a case of trauma presents and the patient is unable to bring the arm closest to the IR up, then the arms and projection could be reversed.