To answer this question, you need to understand the role of the different background processes in an Oracle database.
Option A) PMON - PMON (Process Monitor) is responsible for process cleanup and process recovery. It is not involved in instance recovery.
Option B) SMON - SMON (System Monitor) is responsible for instance recovery. When an instance fails and is restarted, SMON performs crash recovery to bring the database to a consistent state.
Option C) RECO - RECO (Recoverer) is responsible for distributed transaction recovery. It is not involved in instance recovery.
Option D) ARCn - ARCn (Archiver) is responsible for archiving redo log files. It is not involved in instance recovery.
Option E) CKPT - CKPT (Checkpoint) is responsible for signaling the database writer (DBWn) to write dirty buffers to disk and update the checkpoint position in the control file. It is not involved in instance recovery.
The correct answer is B) SMON. SMON performs instance recovery when the database is reopened after an instance failure. It ensures that the database is brought to a consistent state by applying the necessary redo logs.
Therefore, the correct answer is B) SMON.