The student chewed the bread and kept it in test tube and added few drops of Iodine solution

 here`s your answer

Explanation:  the solution will turn blue black colour as the presence of starch in bread and saliva from the mouth the iodine reacts with it and turns it blue black

evidence and logical support is essential for a scientist to do in order to maintain credibility. this is because no one can believe without any logic and without any evidence.hence a scientist can maintain credibility by proving himself and by answering logically so experiments prove very beneficial. logical hypothesis give conclusion which is acceptable. therefore, there are two main factors to maintain credibility by a scientist is evidence and logical support.