Your view wants a list of objects as a model
@model IEnumerable<MVC_ADO.NET_CRUD.Models.Customer>
but you are passing it a single object
Customer objCustomer = new Customer();
...
return View(objCustomer);
You need to decide which is correct, the view or the controller. If your view really needs a list why does the controller only send one object? Either change the view to use a single object as a model
@model MVC_ADO.NET_CRUD.Models.Customer
or change the controller to pass the view a list of objects. As you only have one object you'll need to create a list from that one object, but that's fairly pointless.
return View(new List<Customer> { objCustomer });
If think you might be getting confused with the root model object (Customer) and the fact that it has a List as a property (ShowallCustomer). Maybe you only need the view to have Customer as the model and the code in the view then does
@foreach (var item in Model.ShowallCustomer)