Default feedback messages can be specified in Quiz Properties. However, it's possible to set a custom feedback message for every question.
To enable custom feedback messages:
For the following question categories: Multiple Choice, Yes/No, and Pick One, you can selected the By Answer option and add a custom feedback for a particular answer.
Next, you can edit the message in the popup window. This way, you can add detailed feedback messages. Moreover, you can customize font, size, style and color of your feedback messages; add hyperlinks, bullets and indents.