Date you need to pass like this.
INSERT INTO X VALUES (TO_DATE('1998/05/31 12:00:00', 'YYYY/MM/DD HH24:MI:SS'));
The date format in which the date is stored may be different for a database. So we have to explicitly mention the format of the date/time when we are storing (to_date function with format string). The data will be stored in the format as specified at the database level.