Explanation:

- An agreement restraining trade refers to a contract preventing one party from conducting business, which generally is void under law, as it restricts legal trade rights.

- However, when it comes to the sale of goodwill, such an agreement can be valid within reasonable limits as it protects the buyer's interests.

- Option 1: Void - Completely invalid and unenforceable. This is generally the position of law for restraints on trade but with exceptions in certain contexts like sale of goodwill.

- Option 2: Voidable - Can be voided by one party. This usually applies when consent is affected by factors like misrepresentation or undue influence, not relevant here.

- Option 3: Valid - Enforceable, as the law allows such restriction if it is reasonable and protects the buyer of goodwill.

- Option 4: Contingent - Dependent on a future event. This doesn't directly apply to the basic validity of a restrictive covenant.