Question: In an EFEXT1 (Extension1) Elementary File, if the record type indicates 'additional data' for an ADN/SSC exceeding the 20-digit capacity, how are unused nibbles at the end of the extension data coded?
Option 1: Set to '0' to indicate continuation in another record
Option 2: Set to 'FF' to signify the end of the chain
Option 3: Left blank for future expansions
Option 4: Set to 'F' according to BCD coding conventions
Explanation: When an ADN/SSC exceeds the 20-digit capacity and is stored in EFEXT1 as additional data, the extension data's remaining bytes are coded in BCD. To maintain consistency and indicate unused space, unused nibbles at the end of this extension data must be set to 'F', aligning with standard BCD coding practices for telecommunications.