my radio button is getting cleared on post back

function radio() {
           var m; var n = 0;
           m = parseInt(document.getElementById('<%= hdfcount.ClientID %>').value);

           for (j = 0; j < m; j++) {
               var Section = "CphrEMS_dlquestions_dlsecqustns_" + j;
               var Sectione = document.getElementById(Section);

               for (k = 0; k < Sectione.rows.length; k++) {
                   var Question = Section + "_txtqustn_" + k;
                   var dlOption = document.getElementById(Section + "_dloptions_" + k);
                   var txtlist = dlOption.getElementsByTagName("label");
                   for (l = 0; l < txtlist.length; l++) {
                       var Option = Section + "_dloptions_" + k + "_chkanswer_" + l;
                       document.getElementById(Option).name = k.toString();
                   }
               }
           }
       }

<asp:DataList runat="server" RepeatLayout="Table" ID="dlsecqustns">
                                            <itemtemplate>
                                                <table width="100%">
                                                    <tr>
                                                        <td align="left" width="2%" valign="top" style="padding-removed 25px;">
                                                            <asp:Label runat="server" Text='<%#Eval("qusnum") %>' ID="lblqustn">
                                                        </td>
                                                        <td align="left" width="82%" style="padding-removed 25px;">
                                                            <asp:TextBox ID="txtqustn" runat="server" TextMode="MultiLine" Height="32px" CssClass="textbox"
                                                                Width="70%">
                                                            <ajaxToolkit:TextBoxWatermarkExtender ID="TBWE2"  runat="server" TargetControlID="txtqustn"
                                                                WatermarkText="Question" WatermarkCssClass="watermarked" />
                                                            <asp:FileUpload runat="server" ID="imgqustn" />
                                                            <%--Style="display: none;"--%>
                                                            <br />
                                                            <asp:DataList runat="server" RepeatLayout="Table" ID="dloptions" RepeatDirection="Horizontal"
                                                                RepeatColumns="4">
                                                                <itemtemplate>
                                                                    <table width="99%">
                                                                        <tr>
                                                                            <td width="25%" style="padding: 15px 0 0 0;">
                                                                                <table width="100%">
                                                                                    <tr>
                                                                                        <td align="left">
                                                                                            <asp:Label runat="server" ID="lbloptnum" CssClass="label" Text='<%#Eval("optnum") %>'><span>.</span>
                                                                                            <asp:TextBox runat="server" TextMode="MultiLine" Width="70%" CssClass="textbox" ID="txtoptions"> 
                                                                                           <div  runat="server" id="divrbtn"  önclick="return radiobtn(this.id)">
                                                                                            <asp:RadioButton runat="server" Text="Answer" ID="chkanswer" />
                                                                                             
                                                                                        </td>
                                                                                    </tr>
                                                                                    <tr>
                                                                                        <td align="center" width="25%">
                                                                                            <br />
                                                                                            <input id="uploadFile" style="display: none;" class="textbx"  runat="server" placeholder="Choose File"
                                                                                                disabled="disabled" />
                                                                                            <div id="filediv"  runat="server" style="display: none;" class="fileUpload btn btn-primary">
                                                                                                <span>Upload</span><input id="file"  runat="server"  önchange="CopyMe(this, this.id)"
                                                                                                    type="file" class="upload" />
                                                                                            
                                                                                            <%--Style="display: none;"--%>
                                                                                            <%--<asp:FileUpload runat="server" ID="file" onchange="showimagepreview(this)" />--%><%-- onchange="CopyMe(this, this.id)"--%>
                                                                                        </td>
                                                                                    </tr>
                                                                                </table>
                                                                            </td>
                                                                        </tr>
                                                                    </table>
                                                                </itemtemplate>
                                                            
                                                        </td>
                                                        <td>
                                                            <table>
                                                                <tr>
                                                                </tr>
                                                                <td align="left" width="8%" style="padding-removed 5px;" valign="top">
                                                                    <asp:CheckBox runat="server" onClick="return visibility(this.id)" Text="image" ID="image" />
                                                                </td>
                                                                <tr>
                                                                    <td style="padding-removed 5px;">
                                                                        <asp:Button Text="AddMoreOptions" runat="server" ID="btnaddopt" OnClick="btnaddopt_Click" />
                                                                    </td>
                                                                </tr>
                                                                <tr>
                                                                    <td align="left" style="padding-removed 5px;">
                                                                        <asp:LinkButton ID="ClientButton" OnClientClick=" return v(this.id)" runat="server"
                                                                            Text="Add Question">
                                                                        <ajaxToolkit:ModalPopupExtender ID="mpe"  runat="server" BackgroundCssClass="modalBackground"
                                                                            TargetControlID="ClientButton" PopupControlID="ModalPanel" OkControlID="OKButton" />
                                                                    </td>
                                                                </tr>
                                                            </table>
                                                        </td>
                                                    </tr>
                                                </table>
                                            </itemtemplate>