You created a new user in your database but missed assigning a default tablespace to that user. The user created a table without specifying the tablespace name. In which tablespace would the table…

INDEX is not a standard Oracle-created tablespace and Oracle has no mechanism that designates a tablespace named INDEX as a system-level default for user object placement.

USERS is a common choice for the database default permanent tablespace in many Oracle installations, but the authoritative answer is whichever tablespace is currently set as the database default permanent tablespace - it is not hardcoded to USERS.

SYSAUX is reserved exclusively for Oracle-supplied internal components and optional features and is not available as a default destination for user-created schema objects.

Prior to Oracle 10g, new users without a specified tablespace defaulted to SYSTEM, but Oracle 10g introduced the database-level default permanent tablespace specifically to prevent user objects from polluting SYSTEM.

The default undo tablespace is managed exclusively by Oracle's Automatic Undo Management for storing undo segments and cannot be used to store user tables or other permanent schema objects.

The default temporary tablespace is used only for temporary segments generated by operations such as sorts and hash joins and does not hold permanent objects like user tables.

Since Oracle 10g, every database has a designated default permanent tablespace set via ALTER DATABASE DEFAULT TABLESPACE, which is stored in DATABASE_PROPERTIES. When a user is created without specifying DEFAULT TABLESPACE, Oracle inherits this database-level setting, and any objects that user creates without an explicit tablespace clause are placed there.