Answer: V20
Explanation:
Let's go down the list, shall we?
First, V64. I am going to assume that the V is a square root. If you take the square root of 64 you would get 8, which is not an irrational number.
2/2 would be one of the easiest, its just 1 if you simplify it
(16 would be a rational number, even if you took the square root.
4 is four, a rational number
V20 is an Irrational number, again, assuming that the V is a square root symbol, and you took the square root of it, you would get 4.472135955... an infinite number without a pattern
And 5 is just five, a whole number