You are returning single Alumno entity to view
Alumno p1 = new Alumno();
return View(p1);
And using as list in view.
First clear your requirement. Are you really want to show list on view if not then dont use list in view.
Two option
1. Either remove list from view
2. Pass list of alumno from controller
List<Alumno> p1 = new List<Alumno>();
p1.Add(new Alumno());
return View(p1);