Explanation:

- If there is an error in consensus, it means both parties misunderstood each other, leading to no real agreement.

- Option 1: void – When there is a fundamental error in agreement (consensus ad idem is missing), the contract is void, meaning it has no legal effect from the beginning.

- Option 2: voidable – This applies when an agreement is valid unless one party chooses to void it, like in cases of misrepresentation or undue influence, not a consensus error.

- Option 3: avoid – This is not a relevant legal term.

- Option 4: illegal – This applies when the agreement is against the law, not about error in consensus.