How to Abort completed tasks

it throws an error because 
tasks[i].Status getting always null value and when you want to terminate just write  return keyword


just run this code i make change on it

class Program
    {
        static void Main(string[] args)
        {
            System.Timers.Timer myTimer = new System.Timers.Timer();
            myTimer.Elapsed += new ElapsedEventHandler(OnTimer);
            myTimer.Interval = 1000;
            myTimer.Enabled = true;
            myTimer.AutoReset = false;
            Console.WriteLine(@"Press 'q' and 'Enter' to quit...");
            while (Console.Read() != 'q')
            {
                Thread.Sleep(1000);
            }
        }

        public static void OnTimer(Object source, ElapsedEventArgs e)
        {

            List> tasks = new List>();

            for (int ctr = 1; ctr <= 10; ctr++)
            {
                int baseValue = ctr;
                tasks.Add(Task.Factory.StartNew((b) =>
                {
                    int i = (int)b;
                    return i * i;
                }, baseValue));
            }

            for (int i = 0; i < 10; i++)
            {
                if (tasks[i] != null && (tasks[i].Status == TaskStatus.Running  || tasks[i].Status == TaskStatus.WaitingToRun  || tasks[i].Status == TaskStatus.WaitingForActivation))
                {
                    Console.WriteLine("Task has attempted to start while already running");
                }
                else
                {
                    Console.WriteLine("Task {0} has begun", i);
                    Thread.Sleep(1000);
                }

                if (tasks[i].Status == TaskStatus.RanToCompletion)
                {
                    Console.WriteLine("\n\n\t");
                    Console.WriteLine("Task{0} has completed", i);
                }

            }
            Console.WriteLine();
            Console.WriteLine();
            System.Timers.Timer theTimer = (System.Timers.Timer)source;
            theTimer.Interval += 1000;
            theTimer.Enabled = true;
        }
    }