The correct answer would be: Binary is the only representation used in file formats.
File formats fundamentally operate in binary, as computers process data in binary form (1s and 0s). While binary can be converted to decimal for human readability, and characters can be represented in various encodings (like ASCII or UTF-8 using binary), the underlying format of the file itself remains in binary. Decimal representations are usually just conversions for display purposes, while the actual storage and manipulation of data occur in binary.