Question

how to write action for when an ASP.NET/C# radio button check was changed?
I need a pop up to be opened when radio button is clicked on.

Answer 1

Place the Condition on the OnCheckedChanged Event:

   if(radiobutton.Checked)
   {
      // Place your code for POPUP
      mpeQCAttribute.Show();           // mpeQCAttribute is the ModalPopupExtender
   }