Answer:
Option A.12.8 atm 
Step-by-step explanation:
Step 1:
Data obtained from the question. 
Initial Volume (V1) = 8 L 
Initial pressure (P1) = 0.8 atm
Final volume (V2) = 0.5 L
Final pressure (P2) =? 
Step 2:
Determination of the new pressure. The new pressure of the balloon can simply be obtained by applying the Boyle's law equation as follow:
P1V1 = P2V2 
0.8 x 8 = P2 x 0.5
Divide both side by 0.5
P2 = (0.8 x 8) / 0.5 
P2 = 12.8 atm
Therefore, the new pressure of the balloon is 12.8 atm