Is "A list which its items are 1 and 2" a wrong statement?

Are there any preferences with "A list the items of which are 1 and 2"?

I'm writing a piece of documentation for a program, I want to specify the return value of a function. For sake of simplicity, I've assumed here that the function always returns a list with two items inside (i.e. [1, 2]). For the "Return" part of the documentation, I need a sentence which indicates that

1. The return type is "list"
2. Items of the list are 1 and 2

What I wrote was

Return: A list which its items are 1 and 2

But one of my colleagues believes that

Return: A list the items of which are 1 and 2

is a better representation.

I want to know that:

1. Is the first sentence wrong?
2. Is the second form preferred?