TO KNOW PRIMARY KEY DETAILS

SELECT application_id,
table_id,
primary_key_id,
primary_key_name,
description,
enabled_flag
FROM fnd_primary_keys
WHERE table_id =
(SELECT table_id
FROM fnd_tables
WHERE table_name LIKE UPPER('&table_name'));

Note: Enter the table_name for which you want to find out primary key  details.