Why null is used

Answer 1

Comment to each quiz is at lower left, not upper right.
https://www.sololearn.com/post/131750/?ref=app

Answer 2

I think you are at this lesson
https://www.sololearn.com/learn/JavaScript/2978/
But I don't see a lesson or quiz relating to null.
Which part are you having problem with?

Answer 3

1st example

Answer 4

Oh I see now.
Your question is a good question indeed.
Firstly, let us look at Mozilla Doc:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/apply
The first argument to Function.prototype.apply should be this object.
"You can assign a different this object when calling an existing function. this refers to the current object (the calling object). With apply, you can write a method once, and then inherit it in another object, without having to rewrite the method for the new object."
That's a way of using function with an array to pass into the function as a list arguments, before Spread operator is implemented.