OPen Source I know open source software is that whose source code we can download it and edit it etc. But my question is that if i built an application on open source IDE then that application is also open source e.g I Developed a web application suppose "stack" on asp.netcore mvc then the stack is open source or not.
It depends on the license of the framework you are using, asp .netcore mvc is a framework to assist you in building your application not an IDE. Visual Studio is an Integrated Development Environment.
For example the license for asp.net mvc is available here:
https://github.com/aspnet/Mvc/blob/dev/LICENSE.txt
Typically open source software (project, framework or IDE) does not mandate that your software should also be open source.