Explanation:

- Given word: Incredible

- Means something so extraordinary it is hard to believe or beyond belief.

- Option 1: Unwilling

- Refers to someone who is reluctant or not inclined to do something.

- Does not relate to the believability or extraordinariness of something.

- Option 2: Unbelievable

- Means something that is hard or impossible to believe.

- Perfectly aligns with the meaning of incredible.

- This is the correct choice.

- Option 3: Unnoticed

- Describes something not seen or observed.

- Does not relate to being extraordinary or hard to believe.

- Option 4: Disturbing

- Means something causes distress or anxiety.

- Not related to the concept of being hard to believe.