Introduction :   

Here i will explain How to bind the values into Dropdownlist in and C# in page load. here Values will be passed to dropdownlist from DataSet.

Asp.Net Code :   

<html xmlns="">
<head runat="server">
    <title>Fourth Bottle</title>

    <form id="form1" runat="server">
        <asp:DropDownList ID="DropDownList1" AutoPostBack="false" runat="server">  </asp:DropDownList>

C# Code :       

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
using System.Configuration;
using System.Data.SqlClient;

namespace SolutionName
    public partial class drop : System.Web.UI.Page
        protected void Page_Load(object sender, EventArgs e)
            string Conec = ConfigurationManager.ConnectionStrings["Student"].ConnectionString;
            SqlConnection con = new SqlConnection(Conec);
            SqlDataAdapter da = new SqlDataAdapter("select StudentID from StudentMarks", con);
            DataTable dt = new DataTable();
            DropDownList1.DataSource = dt;
            DropDownList1.DataValueField = dt.Columns["StudentID"].ColumnName.ToString();
            DropDownList1.DataTextField = dt.Columns["StudentID"].ColumnName.ToString();