Which of the following best describes a 'challenge'?

The choice that best describes a 'challenge' is indeed a question raised about someone’s authority. A challenge often involves questioning the validity, ability, or right of someone to hold a particular opinion or position. It can provoke critical thinking and invite deeper discussion, pushing individuals to defend their views or reevaluate their stance. This dynamic reflects the essence of a challenge in various contexts, whether in debates, academics, or personal interactions, as it often requires the challenged party to engage in a justification of their authority or viewpoint.

In contrast, the other options describe concepts that do not capture the essence of a challenge. A statement made in agreement merely reflects consensus and lacks any confrontational or questioning element. Supportive encouragement involves motivating or uplifting someone, which is fundamentally different from the notion of questioning authority. A simple observation, while it may provide factual information, does not inherently provoke debate or indicate a contest of authority.