In the quiz for the Windows Storage Solutions section, question 7 states:
What is the default Allocation Unit Size when formatting a volume?
First, this question does not specify the filesystem. The answer varies depending on the file system.
Secondly, (puts on nerd glasses) the question does not specify the volume size. In one of the lectures in this section, Paul states that the answer is 512 B, but this is incorrect. The default allocation unit size of a volume depends upon the size of the volume. For example, for an NTFS volume of less than 16 TB, the default is 4 KB (source).