Remove .Exe from TaskManager

Question

My  question is whenever i close a running(Windows) application and if  i move to the Windows Task Manager, sometimes the processes gets close, some other times the processes still running in the Task Manager. Can you give me solution on this,whenever i close the application it could also get closed in the Task Manager?. when run Two .exe(Application)

 i used this, but no use

Application.Exit();

Environment.Exit(0);

process.GetCurrentProcess().Kill();

Thanks