Set Default Selected (Checked) value for ASP.Net RadioButton

Hi

I want by default Radio Button should be ticked. I am using below code but it is not working.

<asp:Repeater ID="rptData" runat="server" OnItemDataBound="rptParticipant_ItemDataBound">
    <ItemTemplate>
        <tr>
            <td><asp:Literal ID="ltrlNum" Text="<%# Convert.ToString(Container.ItemIndex + 1) %>" runat="server"></asp:Literal></td>
            <td><asp:Literal ID="ltrlNomineeName" runat="server" Text='<%# Eval("Name") %>'></asp:Literal></td>
            <td><asp:Literal ID="ltrlDesignation" runat="server" Text='<%# Eval("Designation") %>'></asp:Literal></td>
            <td><asp:Literal ID="ltrlPhoneNo" runat="server" Text='<%# Eval("PhoneNo") %>'></asp:Literal></td>
            <td><asp:Literal ID="ltrlEmail" runat="server" Text='<%# Eval("Email") %>'></asp:Literal></td>
            <td class="text-center">
                <div class="btn-group btn-group-toggle" data-toggle="buttons">
                    <asp:RadioButton ID="rb1" runat="server" class="form-check-input-styled"  AutoPostBack="true"  OnCheckedChanged="rbtnSelectEmp_OnCheckedChanged"  /> 
                </div>
            </td>
        </tr>
    </ItemTemplate>
</asp:Repeater>

protected void rbtnSelectEmp_OnCheckedChanged(object sender, EventArgs e)
{
    foreach (RepeaterItem item in rptData.Items)
    {
        RadioButton rbtn = (RadioButton)item.FindControl("rb1");
        rbtn.Checked = false;
    }
    ((RadioButton)sender).Checked = true;
}