Explanation:

- Option 1: Not guilty of theft as the chain was their joint property.

This implies shared ownership but is incorrect as the chain was a personal gift.

- Option 2: Not guilty of theft as the property was temporarily taken away.

Temporary purpose doesn't negate theft if taken without consent.

- Option 3: Guilty of theft.

Z took the chain without consent and intended to permanently deprive the owner of it.

- Option 4: None of the above.

Not applicable as Option 3 correctly identifies the action as theft.