A agrees to pay Rs. 1000 to B if a certain ship returns within a year. However, the ship sinks within the year. In this case, the contract becomes

This is a contingent contract based on a future uncertain event (ship's return). When the event becomes impossible (ship sinks), the contract becomes void. Under Section 32 of the Contract Act, contingent contracts on the happening of an impossible event are void ab initio - they cannot be enforced because the condition can never be fulfilled.