Which of the following terms involves attributing a fault to someone?

The term that involves attributing a fault to someone is "impugn." This word originates from the Latin "impugnare," meaning "to attack" or "to challenge." When you impugn someone's character or motives, you are essentially questioning their integrity or accusing them of wrongdoing. It conveys a sense of doubt or criticism regarding someone's actions or reputation, making it particularly relevant to the idea of attributing fault.

In contrast, "idyll" refers to a simple, peaceful scene, often in nature, and does not relate to fault or accusation. "Fallow" describes land that is left uncultivated and again bears no relevance to attributing fault. "Extirpate" means to remove or eradicate completely, which may involve faults in a different context, but does not imply a direct attribution of fault in the way that "impugn" does. Hence, "impugn" is the best fit for the question posed.