Which of the following is/are true:

given table of necessary condition for 2 Phase Locking system

Key point: All variants of two-phase locking ensure conflict serializability, but only the variant that preclaims all locks is deadlock-free.

• 2PL: Ensures conflict serializability but is not deadlock-free. Locks are requested during execution, so waiting cycles (deadlocks) can occur.

• Conservative 2PL: Acquires all required locks before the transaction starts (preclaim). This prevents waiting cycles, so it is deadlock-free, and because it follows 2PL rules it is conflict serializable. Tradeoff: reduced concurrency.

• Rigorous 2PL: Holds all locks (shared and exclusive) until commit. This gives conflict serializability, recoverability, and cascadelessness, but it is not deadlock-free because locks are still requested during execution rather than preclaimed.

• Strict 2PL: Holds exclusive locks until commit. Ensures conflict serializability and helps with recoverability and preventing cascading aborts, but does not prevent deadlocks.

Conclusion: The only statement that is both conflict serializable and deadlock-free is the one about conservative 2PL, because preclaiming all locks before execution prevents deadlocks while retaining the 2PL serialization guarantees.