Showing sql query results in json format

Question

public class ValuesController : ApiController
    {
        Database_Access_layer.service db = new Database_Access_layer.service();


        public DataSet GetRecord()
        {
            DataSet ds = db.GetRecords();
            return ds;
        }

public class service
   {
       string st = ConfigurationManager.ConnectionStrings["connectionstring"].ConnectionString;
       public DataSet GetRecords()
       {
           SqlConnection con = new SqlConnection(st);
           string adp = "";
           adp = @"select   s.State_Id, RTRIM(s.State_Name) as state_name,count(1) as totalNo







   from  BUyer_details



  inner join Vehicles_Details vd  on BUyer_details.Vehicles_Id=vd.Vehicles_Id

  inner join Model_Registration mr on vd.Model_Code=mr.xEV_Model_Code

  left outer join OEM_Registration om on BUyer_details.OEM_Id = om.OEM_Id



  inner join Dealer_Registration dr  on BUyer_details.Dealer_Id= dr.Dealer_Id

   inner join Mst_Vehicle_Category vc on mr.Vihecle_cat_id=vc.Vihecle_cat_id

inner join tbl_MasterState s on dr.State_Id=s.State_Id

  where 1=1  group by s.State_Name,s.State_Id order by State_Id asc";
           SqlDataAdapter aa = new SqlDataAdapter(adp, con);
           DataSet ds = new DataSet();
           aa.Fill(ds);
           return ds;
       }
   }

I tried creating the query and then returning in json format, but it is showing collections, i want a single array