To check database is in which mode

1. Conn sys/sys as sysdba

2. select log_mode from v$database

To set database in Archivelog mode

1. shutdown immediate;

2. startup mount;

3. alter database archivelog;

4. alter database open;

To set database in NoArchivelog Mode

1. shutdown immediate;

2. startup mount;

3. alter database noarchivelog;

4. alter database open;