C# Online Compiler | .NET Fiddle

using System;
using System.Collections.Generic;
using System.Linq;

namespace ConsoleApplication1
{
    public class Program
    {
        internal class Resident
        {
            public int Id { get; set; }
            public string Name { get; set; }
            public string City { get; set; }
        }


        internal class ResidentNameComparer : IEqualityComparer<Resident>
        {
            public bool Equals(Resident x, Resident y)
            {
                if (string.Equals(x.Name, y.Name, StringComparison.OrdinalIgnoreCase))
                {
                    return true;
                }
                return false;
            }

            public int GetHashCode(Resident obj)
            {
                return obj.Name.GetHashCode();
            }
        }

        public static void Main(string[] args)
        {
            List<Resident> delhiResidents = new List<Resident>();
            delhiResidents.Add(new Resident { Id = 1, Name = "Ramesh", City = "Delhi" });
            delhiResidents.Add(new Resident { Id = 2, Name = "Kapil", City = "Delhi" });
            delhiResidents.Add(new Resident { Id = 3, Name = "Vikas", City = "Delhi" });
            delhiResidents.Add(new Resident { Id = 4, Name = "Amit", City = "Delhi" });

            List<Resident> kolkataResidents = new List<Resident>();
            kolkataResidents.Add(new Resident { Id = 5, Name = "Kapil", City = "Kolkata" });
            kolkataResidents.Add(new Resident { Id = 6, Name = "Manmohan", City = "Kolkata" });
            kolkataResidents.Add(new Resident { Id = 7, Name = "Deepak", City = "Kolkata" });
            kolkataResidents.Add(new Resident { Id = 8, Name = "Amit", City = "Kolkata" });

            var allResidents = delhiResidents.Union(kolkataResidents, new ResidentNameComparer());

            foreach (var item in allResidents)
            {
                Console.WriteLine(item.Name);
            }
        }
    }
}

 
using System;
using System.Collections.Generic;
using System.Linq;
​
namespace ConsoleApplication1
{
    public class Program
    {
        internal class Resident
        {
            public int Id { get; set; }
            public string Name { get; set; }
            public string City { get; set; }
        }
​
​
        internal class ResidentNameComparer : IEqualityComparer<Resident>
        {
            public bool Equals(Resident x, Resident y)
            {
                if (string.Equals(x.Name, y.Name, StringComparison.OrdinalIgnoreCase))
                {
                    return true;
                }

Cached Result

(*)(((*((((*))))(((*(*))))*)))
True
12
12
6