Tone refers to the attitude or emotional quality conveyed by a writer in their text. It can be established through word choice, style, and perspective, and it influences how the reader perceives the content. The correct answer to your question would be:
"The words a writer uses in their text to support their purpose."
Tone reflects the writer's feelings or stance toward the subject matter and can vary from serious, humorous, sarcastic, formal, informal, and more, depending on the context.