using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var arrOld = new List<string>();

        arrOld.Add("InternalScan");

        arrOld.Add("ExternalScan");

        arrOld.Add("ExternalASVScan");

        var arrNew = new List<string>();

        arrNew.Add("InternalScan");

        arrNew.Add("ExternalASVScan");

        var inte = arrNew.Except(arrOld);

        var tup = new Tuple<IEnumerable<string>>(inte);

        if(  tup.Item1.Any())

        {

            Console.WriteLine(tup.Item1.First());

        }

    }

}