Step 1: Understanding the word "flagrant."
"Flagrant" refers to something that is conspicuously offensive or blatant, often referring to actions or behavior that is openly wrong or disgraceful.
Step 2: Analyzing the options.
- Notorious means widely known, especially for something bad, which is similar to "flagrant" in terms of negative publicity, but not the opposite.
- Blatant means obvious and done openly, which is almost synonymous with "flagrant."
- Unobtrusive means not attracting attention, which is the opposite of flagrant because it describes something discreet or not noticeable.
- Adjacent refers to something being next to or adjoining, unrelated to the meaning of flagrant.
Step 3: Conclusion.
"Unobtrusive" is the correct antonym, as it describes something that does not draw attention or stand out, unlike "flagrant," which is designed to do so.
Thus, the correct answer is 3. Unobtrusive.
Final Answer:
\[
\boxed{\text{The correct answer is 3. Unobtrusive.}}
\]