Answer: Option (b) is the correct answer.
Step-by-step explanation:
Chemical techniques help in maintaining the food quality in various ways like they preserve the food, help in removing impurities etc.
For example, pickles are kept safer for longer period of time by the addition of preservatives like sodium benzoate.
Thus, we can conclude that the example of removing excess mercury from a canned tuna product includes a chemical technique of improving food quality.