The question gives the impression that the source files were held at /u01/app/oracle/oradata, but are now physically located at /u01/app/oracle/oradata. The xml description file is still at
/u01/app/oracle/oradata/pdb1.xml
A: FALSE - SOURCE_FILE_NAME_CONVERT is only needed if the XML file does not accurately describe the current location of the pdb's files.
B: FALSE - If pdb1 ran correctly before, it will run correctly now - assuming that no major upgrade of CDB1 has happened.
C: FALSE - PDB_FILE_NAME_CONVERT is needed only when OMF is not used. The question tells us that OMF is enabled.
D: TRUE - The use of the SOURCE_FILE_NAME_CONVERT parameter indicates that the DB files have been moved, so the xml file does not hold the correct locations E: TRUE - Unplugging a database will result in the PDB remaining in a MOUNT state. It is still part of the CDB and will still be backed up etc... After unplugging, a PDB needs to be dropped before a new PDB can be created with the same name.