list data validation automation excel

Question

I am automating excel from c# and want to put list data validation on a column I have so far:

//Creat Excel WorkBook with WorkSheet 

            Excel.Application objExcel = new Excel.Application();

            Excel.Workbook objWorkBook = objExcel.Workbooks.Add(System.Reflection.Missing.Value);

            Excel.Worksheet objSheet = (Excel.Worksheet)objWorkBook.Worksheets.get_Item(1);

            //put column heading in row 1

            objSheet.get_Range("a1", System.Reflection.Missing.Value).Value2 = "rs_id";

            objSheet.get_Range("b1", System.Reflection.Missing.Value).Value2 = "manufacturer";

            objSheet.get_Range("c1", System.Reflection.Missing.Value).Value2 = "title";

            objSheet.get_Range("d1", System.Reflection.Missing.Value).Value2 = "description";

            objSheet.get_Range("e1", System.Reflection.Missing.Value).Value2 = "quantity";

            objSheet.get_Range("f1", System.Reflection.Missing.Value).Value2 = "discrepancy";

            objSheet.get_Range("g1", System.Reflection.Missing.Value).Value2 = "cost_price";

            objSheet.get_Range("h1", System.Reflection.Missing.Value).Value2 = "BIN_price";

            objSheet.get_Range("i1", System.Reflection.Missing.Value).Value2 = "quantity_per_sale";

            objSheet.get_Range("j1", System.Reflection.Missing.Value).Value2 = "category";

            //find out how many need to be preped befor the can be listed

            SqlDataAdapter DaFindNumberToPrep = new SqlDataAdapter();

            DataSet DsToPrep = new DataSet();

            string SelectToPrep = "SELECT * FROM test_db.dbo.deliveries WHERE ready_to_list = 'no'";

            int NumberToPrep = 0;

            using (SqlConnection test_db_conn = new SqlConnection(test_db_ConnectionStrin))

            {

                DaFindNumberToPrep = new SqlDataAdapter(SelectToPrep, test_db_conn);

                DaFindNumberToPrep.Fill(DsToPrep);

                NumberToPrep = (int)DsToPrep.Tables[0].Rows[0][0];

            }

            //loop to populate sheet

            int row_index = 2;

            foreach (DataRow row in DsToPrep.Tables[0].Rows)

            {

                objSheet.get_Range("a" + row_index.ToString(), System.Reflection.Missing.Value).Value2 = row["rs_id"].ToString();

                objSheet.get_Range("b" + row_index.ToString(), System.Reflection.Missing.Value).Value2 = row["manufacturer"].ToString();

                objSheet.get_Range("c" + row_index.ToString(), System.Reflection.Missing.Value).Value2 = row["title"].ToString();

                objSheet.get_Range("d" + row_index.ToString(), System.Reflection.Missing.Value).Value2 = row["description"].ToString();

                objSheet.get_Range("e" + row_index.ToString(), System.Reflection.Missing.Value).Value2 = (int)row["quantity"];

                objSheet.get_Range("f" + row_index.ToString(), System.Reflection.Missing.Value).Value2 = row["discrepancy"].ToString();

                objSheet.get_Range("g" + row_index.ToString(), System.Reflection.Missing.Value).Value2 = (float)row["cost_price"];

                row_index++;

            }

            //Display results

            objExcel.Visible = true;

but once the loop is done I want to set "j2":"j"+row_index.ToString() to have list data validations ie it can only take the values in the range "k1":"k6" so that the user can just choose from the drop down list