Complete ASPX HTML Source Codes:- <%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default8.aspx.cs" Inherits="Default8" %> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head id="Head1" runat="server"> <title></title> <script src="//code.jquery.com/jquery-1.11.1.min.js" type="text/javascript"></script> <script type="text/javascript"> function ShowHideDiv() { //Get dropdown selected value var SelectedValue = $('#<%= ddlPaymentMode.ClientID %> option:selected').val(); // check selected value. if (SelectedValue == 0) { alert('Please ..