Which one of the following combinations is incorrect?

Answer: Wheedle - Roundabout

Explanation:

• Acquiescence - Submission: Both words refer to yielding or accepting quietly; they are synonyms.

• Wheedle - Roundabout: "Wheedle" means to coax or persuade by flattery or cajoling. "Roundabout" means indirect. These meanings do not match, so this pairing is incorrect. A correct synonym for "wheedle" would be "coax" or "cajole."

• Flippancy - Lightness: "Flippancy" denotes levity or a lack of seriousness, which aligns with the idea of "lightness" in tone. They are acceptable synonyms, though "flippancy" can have a more negative nuance.

• Profligate - Extravagant: "Profligate" describes someone who is recklessly wasteful or excessively extravagant, so it matches "extravagant."

Conclusion: The incorrect combination is Wheedle - Roundabout because the meanings do not correspond.