function LoadData(id) {
var employeeId = $.trim($("#employeeId").val());
var employeeType = $.trim($("#employeeType").val());

var obj = "";
var CityId = $.trim($("#ddlCity").val());
obj = new ViewModel1(employeeId, employeeType, 0, $.trim($("#DeptName").val()), "", "", $.trim($("#SectionName").val()), CityId);
var postedData = JSON.stringify(obj);

Loader();
$.ajax({
    //...........
    //...........
})

@Html.DropDownGroupListFor(m => m.CityId, Model.GroupedTypeOptions, new { name = "ddlCity", id = "ddlCityName", @onchange = "javascript:LoadData(this.value)" })