Answer:
Appeal to Credibility.
Step-by-step explanation:
Ethos or an appeal to credibilty is a persuasive approach that appeals to the credibility or reliablity of the speaker. In this approach of persuasion, the audience sees how much a person or the speaker can be trusted. Is the speaker of good reputation? Is he trustworthy? etc.
The given scenario exemplifies an appeal to credibility of the speaker. As the audience is persuaded about the medicines seeeing the doctor's white coat. The viewers of these advertisements will see the doctor's white coat and will be persuaded that the endorsement is credible as a doctor is recommending the product or the medicine.
So, the correct answer is an appeal to credibility.