Program:

The source code to demonstrate the Linq Union() method with StringComparer, is given below. The given program is compiled and executed successfully on Microsoft Visual Studio.

//C# Program to demonstrate Linq Union() method 
//with StringComparer.

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

class Demo
{
    static void Main(string[] args)
    {
        List<string> List1 = new List<string>() { "Abc", "Pqr", "Lmn", "Xyz" };
        List<string> List2 = new List<string>() { "Abc", "pqr" , "KLP" };

        var result = List1.Union(List2, StringComparer.OrdinalIgnoreCase);

        foreach (var value in result)
        {
            Console.WriteLine(value + " ");
        } 
    }
}

Output:

Abc
Pqr
Lmn
Xyz
KLP
Press any key to continue . . .

Explanation:

In the above program, we created two lists of integer numbers that are given below.

List<string> List1 = new List<string>() { "Abc", "Pqr", "Lmn", "Xyz" };
List<string> List2 = new List<string>() { "Abc", "pqr" , "KLP" };

Here we used Linq Union() method to perform union operation by ignoring case between two lists using the below code.

var result = List1.Union(List2, StringComparer.OrdinalIgnoreCase);

Then we print the result on the console screen using the below code using the "foreach" loop.

foreach (var value in result)
{
    Console.WriteLine(value + " ");
}