Asp.net Web service return json format data

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Services;
using System.Web.Script.Serialization;
using System.Web.Script.Services;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;
using System.ComponentModel;
 

namespace Webservice
{
    
    [WebService(Namespace = "http://tempuri.org/")]
    [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
    [ToolboxItem(false)]
    // To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line. 
    // [System.Web.Script.Services.ScriptService]
    public class Service1 : System.Web.Services.WebService
    {
        public Service1()
        {
            //Uncomment the following line if using designed components 
            //InitializeComponent(); 
        }
        [WebMethod]
        [ScriptMethod(ResponseFormat = ResponseFormat.Json)]
        
        public Void GetEmployees()
        {
            System.Web.Script.Serialization.JavaScriptSerializer serializer = new System.Web.Script.Serialization.JavaScriptSerializer();
            
            SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["NSConstr"].ToString());
            SqlCommand cmd = new SqlCommand();
            cmd.CommandText = "SELECT *  FROM Contact e ";
            DataSet ds = new DataSet();
            DataTable dt = new DataTable();
            SqlDataAdapter da = new SqlDataAdapter(cmd);
            da.SelectCommand.Connection = con;
            da.Fill(dt);
            con.Close();
            
            List<Dictionary<string, object>> rows = new List<Dictionary<string, object>>();
            Dictionary<string, object> row = null;
            foreach (DataRow rs in dt.Rows)
            {
                row = new Dictionary<string, object>();
                foreach (DataColumn col in dt.Columns)
                {
                    row.Add(col.ColumnName, rs[col]);
                }
                rows.Add(row);
            }
 
           this.Context.Response.ContentType = "application/json; charset=utf-8";
     this.Context.Response.Write(serializer.Serialize(new { Cargo = rows }));
        }     
 
        public string errmsg(Exception ex)
        {
            return "[['ERROR','" + ex.Message + "']]";
        }
    }
}

Quote:

Here is my output:(i'm not getting xml strings)

{"Cargo":[{"Id":1,"FirstName":"devi","LastName":"priya ","Contactno":"965577796 "},{"Id":2,"FirstName":"arun","LastName":"kumar","Contactno":"9944142109"},{"Id":3,"FirstName":"karu","LastName":"ronald","Contactno":"8883205008"}]}