using System.Collections.Generic;

using System.Linq;

​

public static class Program

{

    public static void Main(string[] args)

    {

        var n1 = new List<int>() { 1, 2, 3, 4 };

        var n2 = new List<int>() { 4, 3, 5, 6 };

        var n4 = new List<char>() { '1', '2', 'a', 'b', 'c', 'd' };

        int maxLength = new[] {n1.Count, n2.Count, n4.Count}.Max();

        var n5 = (from i in Enumerable.Range(0, maxLength)

                  select new

                  {

                      i1 = n1.IndexOrDefault(i),

                      i2 = n2.IndexOrDefault(i),

                      i3 = n4.IndexOrDefault(i)

                  }).AsParallel().ToList();

    }

    private static T IndexOrDefault<T>(this IList<T> col, int index)

    {

        return index < col.Count ? col[index] : default(T);

    }

}

​