Explanation:

- Flexible refers to the ability to bend or adapt easily without breaking.

- Option 1: Compliant means being inclined to agree with others or obey rules. It implies flexibility and willingness to adapt.

- Option 2: Defiant means boldly resisting or challenging, suggesting a refusal to adapt or change.

- Option 3: Peculiar means strange or unusual, which is not related to flexibility.

- Option 4: Reckless means acting without thinking or caring about the consequences and is unrelated to being flexible.

The most appropriate antonym for "Flexible" is Defiant.