Client Side Required Validator using Validation Group

For TextBox

 <asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" ControlToValidate="txtBudgetNo" ErrorMessage="Please Enter Budget no"  Display="Dynamic"  ValidationGroup="s" ></asp:RequiredFieldValidator>



For DropDownList

 <asp:RequiredFieldValidator ID="RequiredFieldValidator3" runat="server"
        ControlToValidate="ddlfinancialYear" ErrorMessage="Please Select Financial Year" Display="Dynamic"  ValidationGroup="s" InitialValue="0"></asp:RequiredFieldValidator>