How to Validate Drop Down List

Question

<td style="width: 712px; text-align: left; margin:10px; height: 50px;">

<asp:DropDownList ID="DropDownListNewEmployeeRegisterationFormStates" runat="server" Width="226px" Height="33px" OnSelectedIndexChanged="DropDownListNewEmployeeRegisterationFormStates_SelectedIndexChanged" AutoPostBack="true" DataTextField="StateNames" DataValueField="StateID">

</asp:DropDownList>

</td>

<td style="width: 45%; text-align: left; height: 50px;">

<asp:RequiredFieldValidator ID="RequiredFieldValidatorNewEmployeeRegisterationFormStates" runat="server" ControlToValidate="DropDownListNewEmployeeRegisterationFormStates" InitialValue="0" ErrorMessage="Please Select State Name" ForeColor="Red" Display="Dynamic" SetFocusOnError="true"></asp:RequiredFieldValidator>

</td>

</tr>

<tr>

<td style="width: 20%; text-align: left; height: 50px;"><h3>City of Resident : </h3></td>

<td style="width: 712px; text-align: left;margin:10px; height: 50px;">

<asp:DropDownList ID="DropDownListNewEmployeeRegisterationFormCity" runat="server" Width="225px" Height="28px" OnSelectedIndexChanged="DropDownListNewEmployeeRegisterationFormCity_SelectedIndexChanged" AutoPostBack="true" DataTextField="CityNames" DataValueField="CityID">

</asp:DropDownList>

</td>

<td style="width: 45%; text-align: left; height: 50px;">

<asp:RequiredFieldValidator ID="RequiredFieldValidatorNewEmployeeRegisterationFormCity" runat="server" ControlToValidate="DropDownListNewEmployeeRegisterationFormCity" InitialValue="0" ErrorMessage="Please Select City Name" ForeColor="Red" Display="Dynamic" SetFocusOnError="true"></asp:RequiredFieldValidator>

</td>