- DB/2: This is not an operating system; DB/2 is actually a database management system (DBMS) developed by IBM.
- LINUX: This is an operating system, specifically a popular open-source Unix-like system.
- OS/2: This is also an operating system developed by IBM and Microsoft.
- Android: This is a mobile operating system developed by Google.
Therefore, the correct answer is 1. DB/2.