Correct Answer: Empirical

Solution : The correct answer is the fourth option.

The word "empirical" is used to describe the nature of the evidence and experimentation supporting the scientist's hypothesis. The term "empirical" describes information derived from observation, experience, or experimentation. It is closely related to the idea of being factual, as it emphasises information grounded in real-world observations and data.

The meanings of the other options are as follows:

• Rigorous: thorough and precise, emphasising strict accuracy.
• Hypothesis: a proposed explanation based on limited evidence, a tentative idea.
• Evidence: facts or information indicating the truth or validity of a belief or proposition.

Therefore, the correct answer is empirical.