Generics - General Questions

What is the output of the following program?

var words = new List<string> { "kiwi", "fig", "banana" };
Console.WriteLine(string.Join(",", words.OrderBy(w => w.Length)));

What is the output of the following program?

var stack = new Stack<string>();
stack.Push("a"); stack.Push("b");
Console.WriteLine(stack.Pop() + stack.Count);

What is the output of the following program?

var set = new HashSet<int> { 1, 2, 2, 3 };
Console.WriteLine(set.Count);

Which constraint requires T to be a reference type?

What is the benefit of generics such as List<T> over ArrayList?