How to Validate Dynamic DropDownList in ASP.Net

Hi sir,

How to validate dynamic dropdownlist in asp.net c# country names are coming from database.

 public void Bind_ddlCountry()
    {

        SqlConnection con = new SqlConnection(ConnString);

        con.Open();

        SqlCommand cmd = new SqlCommand("select id, CountryName from countries", con);

        SqlDataReader dr = cmd.ExecuteReader();

        ddlcountry.DataSource = dr;

        ddlcountry.Items.Clear();

        ddlcountry.Items.Add("Please Select Country");

        ddlcountry.DataTextField = "CountryName";

        ddlcountry.DataValueField = "id";

        ddlcountry.DataBind();

        con.Close();

    }

<tr>
    <td align="right">Country</td>  
    <td>
    
    <asp:UpdatePanel ID="countrypanel" runat="server">

          <ContentTemplate >

             <asp:DropDownList CssClass="form-control" ID="ddlcountry" 
             AutoPostBack ="true" AppendDataBoundItems="true" runat="server" 
                  onselectedindexchanged="ddlcountry_SelectedIndexChanged" >
       </asp:DropDownList>
       
 

       </ContentTemplate>

 

     <Triggers>

      <asp:AsyncPostBackTrigger ControlID ="ddlcountry" />

     </Triggers>

  </asp:UpdatePanel></td>
         
      
  </tr>