In the sentence "the ball is red," red is a __________________ of the ball.

In the context of the sentence "the ball is red," the correct fill-in is "attribute." An attribute is a characteristic that describes an object, often outlining a specific quality or feature that helps to identify or categorize that object. In this case, "red" describes a specific quality of the ball, indicating its color, which is a fundamental aspect of how we perceive and understand the object.

While other options also relate to aspects of description, "attribute" is a term that encompasses any defining quality, making it a more precise choice in this context. The use of the term in behavioral analysis often refers to specific defining characteristics of a subject, which aligns well with how "red" defines the ball.