Answer:
Tube 3
Explanation:
Pancreatic amylase's optimum pH is basic, NaHCO3 is a base so it will provide the optimum pH for the enzyme to catalyse the breakdown of starch.
In tube 1 there will not be the breakdown of starch as there simply isn't any enzyme to break it down.
In Tube 2, the enzyme pancreatic amylase will most probably become denatured (loss of shape), as HCl is acidic which causes it to lose shape causing a change in the active site and will never be able to catalyse the breakdown of starch.
Hope this helps :)