How to validate the current wizard using C#

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C#

ASP

.NET

In my application i have a wizard control where i will get the steps in wizard after loading the application firstly i will get wizard 1 then if i click next button i will get wizard 2 with second question my requirement is i need to check if a radio button for first question is selected or not if user clicks next button with selecting first radio button then i need to show a msg that first question should be answered first on a condition without going to second question other wise if a radio button is selected for first question then there is no need of showing the message how can i do this

<pre><asp:Wizard ID="Wizard1" runat="server" DisplaySideBar="false" onnextbuttonclick="Wizard1_NextButtonClick" onfinishbuttonclick="Wizard1_FinishButtonClick" >
           <WizardSteps>
               <asp:WizardStep ID="WizardStep1" runat="server" Title="Step 1">
                <div class="content">
                <table>
                <tr><td style="width:136px; text-align:center"></td><td style="width:800px; text-align:left;"></td></tr>
                    <tr><td style="width:136px; text-align:center"></td><td style="width:800px; text-align:left;"></td></tr>
                    <tr><td style="width:136px; text-align:center; color:#C57808; font-weight:bold;">Q 01</td><td style="width:800px; text-align:left; padding-left:8px; font-weight:bold; font-size:18px; color:#C57808;">What will be the time now</td></tr>
                    <tr><td style="width:136px; text-align:center"></td><td style="width:800px; text-align:left; padding-left:100px; font-size:17px; color:Green; font-family:@Gulim;">A. <asp:RadioButton ID="rb1A" GroupName="g1" runat="server" Text="Ans1" /> </td></tr>
                    <tr><td style="width:136px; text-align:center"></td><td style="width:800px; text-align:left; padding-left:100px; font-size:17px; color:Green; font-family:@Gulim;">B. <asp:RadioButton ID="rb1B" GroupName="g1" runat="server" Text="Ans2" /> </td></tr>
                    <tr><td style="width:136px; text-align:center"></td><td style="width:800px; text-align:left; padding-left:100px; font-size:17px; color:Green; font-family:@Gulim;">C. <asp:RadioButton ID="rb1C" GroupName="g1" runat="server" Text="Ans3" /> </td></tr>
                    <tr><td style="width:136px; text-align:center"></td><td style="width:800px; text-align:left;"></td></tr>
                    <tr><td style="width:136px; text-align:center"></td><td style="width:800px; text-align:left;"></td></tr>
                    <tr><td style="width:136px; text-align:center"></td><td style="width:800px; text-align:left;"></td></tr>
                    <tr><td style="width:136px; text-align:center"></td><td style="width:800px; text-align:left;">
                </table>
                </div>
               </asp:WizardStep>
               <asp:WizardStep ID="WizardStep2" runat="server" Title="Step 2">
                   <div class="content">
                    <table style="width:936px; height:450px; border:1px solid black; vertical-align:top; font-family:Verdana; font-size:15px; ">                    
                        <tr><td style="width:136px; text-align:center"></td><td style="width:800px; text-align:left;"></td></tr>
                        <tr><td style="width:136px; text-align:center"></td><td style="width:800px; text-align:left;"></td></tr>
                        <tr><td style="width:136px; text-align:center; color:#C57808; font-weight:bold;">Q 02</td><td style="width:800px; text-align:left; padding-left:8px; font-weight:bold; font-size:18px; color:#C57808;">How should i complete this</td></tr>
                        <tr><td style="width:136px; text-align:center"></td><td style="width:800px; text-align:left; padding-left:100px; font-size:17px; color:Green; font-family:@Gulim;">A. <asp:RadioButton ID="rb2A" GroupName="g2" runat="server" Text="Will I" /> </td></tr>
                        <tr><td style="width:136px; text-align:center"></td><td style="width:800px; text-align:left; padding-left:100px; font-size:17px; color:Green; font-family:@Gulim;">B. <asp:RadioButton ID="rb2B" GroupName="g2" runat="server" Text="Do I" /> </td></tr>
                        <tr><td style="width:136px; text-align:center"></td><td style="width:800px; text-align:left; padding-left:100px; font-size:17px; color:Green; font-family:@Gulim;">C. <asp:RadioButton ID="rb2C" GroupName="g2" runat="server" Text="Can i" /> </td></tr>
                        <tr><td style="width:136px; text-align:center"></td><td style="width:800px; text-align:left;"></td></tr>
                        <tr><td style="width:136px; text-align:center"></td><td style="width:800px; text-align:left;"></td></tr>
                        <tr><td style="width:136px; text-align:center"></td><td style="width:800px; text-align:left;"></td></tr>
                        <tr><td style="width:136px; text-align:center"></td><td style="width:800px; text-align:left;"></td></tr>
                    </table>
                   </div>
               </asp:WizardStep>
          </WizardSteps>
           <HeaderTemplate>
               <ul id="wizHeader">
                   <asp:Repeater ID="SideBarList" runat="server">
                       <ItemTemplate>
                           <li><a class="<%# GetClassForWizardStep(Container.DataItem) %>" title="<%#Eval("Name")%>">
                               <%# Eval("Name")%></a> </li>
                       </ItemTemplate>
                   </asp:Repeater>
               </ul>
           </HeaderTemplate>
       </asp:Wizard>

protected void Wizard1_PreRender(object sender, EventArgs e)
{
Repeater SideBarList = Wizard1.FindControl("HeaderContainer").FindControl("SideBarList") as Repeater;
SideBarList.DataSource = Wizard1.WizardSteps;
SideBarList.DataBind();
}
protected string GetClassForWizardStep(object wizardStep)
{
WizardStep step = wizardStep as WizardStep;

if (step == null)
{
return "";
}
int stepIndex = Wizard1.WizardSteps.IndexOf(step);

if (stepIndex < Wizard1.ActiveStepIndex)
{
return "prevStep";
}
else if (stepIndex > Wizard1.ActiveStepIndex)
{
return "nextStep";
}
else
{
return "currentStep";
}
}
protected void Wizard1_NextButtonClick(object sender, WizardNavigationEventArgs e)
{
}

What I have tried:

i tried by using if else condition to validate whether radio buttons are checked or not when we click next button but if user does not select any radio button i am returning there it self but still it is executing Wizard1_PreRender and GetClassForWizardStep methods