Getting data from database using wcfresr service?

INterface:
[ServiceContract]
    public interface IStudentData
    {
        [OperationContract]
        [WebInvoke(UriTemplate="Allstudents", ResponseFormat = WebMessageFormat.Json)]
        List<ListItem> GetStudents();
    }

Class:

public List<ListItem> GetStudents()
        {
            string connstr = ConfigurationManager.ConnectionStrings["Resrservice"].ToString();
            SqlConnection con = new SqlConnection(connstr);
            SqlCommand cmd = new SqlCommand();
            cmd.CommandText = "select RollNo,Name from Student";
            cmd.Connection = con;
            SqlDataAdapter da = new SqlDataAdapter(cmd);
            DataSet ds = new DataSet();
            con.Open();
            da.Fill(ds, "Student");
            con.Close();
            List<ListItem> stulist = new List<ListItem>();
            if (ds.Tables != null)
            {
                int re = ds.Tables["Student"].Rows.Count;
                if (re > 0)
                {
                    DataTable dtab = ds.Tables["Student"];
                    for (int i = 0; i < re; i++)
                    {
                        stulist.Add(new ListItem(
                            dtab.Rows[i]["Name"].ToString(),
                            dtab.Rows[i]["RollNo"].ToString()
                    ));
                    }
                }
            }
            cmd.Dispose();
            return stulist;
        }
Confiq file:

<?xml version="1.0"?>
<configuration>

  <appSettings>
    <add key="aspnet:UseTaskFriendlySynchronizationContext" value="true" />
    
  </appSettings>
  <connectionStrings>
    <add name="Resrservice" connectionString="Data Source=NOTOUSANIL\SQLEXPRESS;Initial Catalog=REST;Persist Security Info=True;User ID=sa;Password=123"/>
  </connectionStrings>
  <system.web>
    <compilation debug="true" targetFramework="4.5" />
    <httpRuntime targetFramework="4.5"/>
  </system.web> 
  <system.serviceModel>
    <services>
      <service name="WcfService.StudentData">
        <endpoint address="" binding="webHttpBinding" behaviorConfiguration="restPoxBehavior" contract="WcfService.IStudentData"/>
      </service>
    </services>
    <behaviors>
      <serviceBehaviors>
        <behavior>
          <!-- To avoid disclosing metadata information, set the value below to false before deployment -->
          <serviceMetadata httpGetEnabled="true"/>
          <!-- To receive exception details in faults for debugging purposes, set the value below to true.  Set to false before deployment to avoid disclosing exception information -->
          <serviceDebug includeExceptionDetailInFaults="false"/>
        </behavior>
      </serviceBehaviors>
      <endpointBehaviors>
        <behavior name="restPoxBehavior">
          <webHttp helpEnabled="true"/>
        </behavior>
      </endpointBehaviors>
    </behaviors>
    <serviceHostingEnvironment multipleSiteBindingsEnabled="true"/>
  </system.serviceModel>
  <system.webServer>
    <modules runAllManagedModulesForAllRequests="true"/>
    <!--
        To browse web app root directory during debugging, set the value below to true.
        Set to false before deployment to avoid disclosing web app folder information.
      -->
    <directoryBrowse enabled="true"/>
  </system.webServer>

</configuration>

After i a running this service

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