Is paper boxes biodegradable

Usually. "Corrugated" is simply the process where a sheet of cardboard is made of 3 (or more) individual pieces: Two pieces form the walls while the third runs sort of zig-zag between them. Most cardboard available today is going to be corrugated.

However, there are other processes (like lamination) which will make it hard, if not impossible for the cardboard to degrade.