Final answer:
Amylase has an optimum pH near neutrality, with salivary amylase having an optimum around pH 7.0. It does not work more effectively in highly acidic or alkaline conditions, so it would be most active in a pH 7.0 buffer solution like Tube 3.
Step-by-step explanation:
The enzyme amylase is known to act on starch and is present in various secretions of the digestive system like saliva and pancreatic juice. Based on the provided information, amylase exhibits different levels of activity under different pH conditions.
When examining the activity of amylase at different pH levels, it is noted that the enzyme has an optimum pH near neutrality, which typically ranges around pH 7.0 for salivary amylase and slightly higher for pancreatic amylase. The activity of the enzyme tends to decrease as the pH moves away from this optimal range. Hence, for the given test tubes - Tube 3 with a pH 7.0 buffer, Tube 7 with a pH 2.0 buffer, and Tube 8 with a pH 9.0 buffer - the activity of amylase would be expected to be highest in Tube 3.
Given these observations, the correct answer would be that amylase works optimally at pH 7.0. The other options are incorrect because amylase's activity is indeed affected by pH, and it does not become more active in overly acidic or alkaline conditions.