Explanation:
only the second one fulfills the rule that every value of x must have exactly 1 assigned result value (y).
the first option has two different result values (3 and 5) for x = 1.
the third has 2 different result values (3 and 4) for x = 2.
the fourth has 2 different result values (2 and 4) for x = 2, and also 2 different result values (0 and 2) for x = 0.