Final answer:
The purpose of the article is the best indicator of a source's validity.
Step-by-step explanation:
The best indicator of a source's validity is the purpose of the article. When evaluating a source, it is important to consider whether the information relates to your topic or supports your thesis. Additionally, consider the intended audience of the source and the author's purpose for creating it. If a source's purpose aligns with your research needs and presents information in a neutral and unbiased manner, it is likely to be a valid source.