Question1_HashSet.cs

var hashSet = new HashSet<string>(StringComparer.OrdinalIgnoreCase);

hashSet.Add("abc");
hashSet.Add("Abc");
hashSet.Add("abc");
hashSet.Remove("ABC");
hashSet.Add("abc");

Console.WriteLine(hashSet.Count);

Question2_Async.cs

using System.Net.Http;
using System.Threading.Tasks;
using System.Windows;

namespace WpfApplication1
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        // explain how this code will behave
        private void button_Click(object sender, RoutedEventArgs e)
        {
            string result = GetImportantStuffAsync().Result;
            MessageBox.Show(result);
        }

        private async Task<string> GetImportantStuffAsync()
        {
            var httpClient = new HttpClient();

            string response = await httpClient.GetStringAsync("https://google.com");

            DoStuffWithResponse(response);

            return response;
        }

        private void DoStuffWithResponse(string response)
        {
            // do something important here
        }
    }
}

Question3_Lock.cs

namespace ConsoleApplication26
{
    public class ImportantClass
    {
        private static object _lock = new object();

        public void SomeMethod()
        {
            int integer = 5;

            //please explain this.
            lock (integer)
            {
                DoStuff();
            }

            object obj = integer;

            //please explain this.
            lock (obj)
            {
                DoStuff();
            }

            //please explain this.
            lock (this)
            {
                DoStuff();
            }

            //please explain this.
            lock (_lock)
            {
                DoStuff();
            }
        }

        private static void DoStuff()
        {
            //some important work here
        }
    }
}

Question4_Powershell.ps1

$folderPath = "D:\input"

#write powershell that will get all the files that have "txt" extension (e.g. file with name 'a.txt' but not 'abctxt) and file length > 5

Question5_Coding.cs

namespace ConsoleApplication26
{
    public class Program
    {
        //given a string input - find the "word" that occures the most
        //example 1: input "a a a b b c c", output: "a"
        //example 2: input "what are you doing? do you like tht?", output: "you"
        public string GetWordWithMaxOccurance(string input)
        {
            //write your code here
        }
    }
}

Question6_Closure.js

for (var i = 0; i < 3; i++) {
      setTimeout(function(){ console.log("i: " + i); }, i + 1000);
}