Your database is having two control files; three redo log file groups with two members in each group. Failure of which file would cause a instance to shut down?

Control files contain critical metadata about the database structure and are essential for database operation. If any control file is lost, the database instance will shut down because it cannot access the necessary information to manage the database. While Oracle recommends multiplexing (having multiple control files), losing one affects the database's ability to function. The other options - parameter file, redo log members, data files, and archive logs - have different failure characteristics that don't always cause immediate shutdown.