The most appropriate antonym of the word "tasty" in the given sentence is:

Option 3: bland

Explanation: In the context of the sentence, "tasty" describes the quality of the pickles made by the grandmother, indicating they are flavorful and enjoyable. The antonym should convey the opposite meaning, which would be something lacking flavor or taste. Option 3, "bland," fits this description as it means lacking strong or distinctive flavor. Therefore, option 3 is the most appropriate antonym for "tasty" in this context.