It looks like your model object would be single object for this view but you are binding your view with
IPagedList<Popr.Data.C_QuestionTable>
which is a collection not single item.
So, you need to set your model to be :
@model Popr.Data.C_QuestionTable
and now you should be able to access the property :
<pre> @Html.DropDownListFor(model => model.ClassID, (SelectList)ViewBag.dataForDropDowns, new { @class = "form-control select2ddl" })