Explanation:

- Ludicrous: It means something that is absurd, ridiculous, or laughable because of being implausible or exaggerated.

- Option 1: Intuitive: Relating to the ability to understand something instinctively, without the need for deliberate reasoning. Not a synonym for ludicrous.

- Option 2: Intrinsic: Referring to the essential nature or innate quality of something. Totally unrelated to ludicrous.

- Option 3: Astute: Describes someone who has sharp judgment or keen perception. This doesn't align with the meaning of ludicrous.

- Option 4: Crazy: This term can mean wildly unreasonable or foolish, which is similar to ludicrous.

The most appropriate synonym for ludicrous is:

- Option 4: Crazy