Answer:
2). The source's relevance to your research topic.
Step-by-step explanation:
The most significant factor to determine a source's usefulness would be 'it's relevance to the research topic' that one is investigating. The content or information offered by the source must address the topic, relate to it, or answer the research question. It needs to offer facts and opinions that are significant to elaborate and justify the research topic. The accuracy and credibility of the source always come the second as relevance is the priority. If a source is not relevant to explain or elucidate your topic, it is futile. Thus, option 2 is the correct answer.