Which ACID property ensures that a transaction is executed entirely or not…

Correct answer: Atomicity.

Atomicity is the ACID property that guarantees a transaction is treated as a single, indivisible unit of work — it is either executed entirely (all of its operations commit) or not executed at all. It is popularly called the “all-or-nothing” rule.

If a failure (system crash, power loss, error, or explicit abort) occurs midway through a transaction, the recovery mechanism rolls back every change the transaction has already made, so no partial updates are left permanently in the database. The classic example is a fund transfer: debiting account A and crediting account B must both succeed; if the credit fails after the debit, atomicity ensures the debit is undone so money is never lost.

The other ACID properties solve different problems: Consistency keeps the database in a valid state with respect to all rules and constraints, Isolation keeps concurrently running transactions from interfering with one another, and Durability guarantees that once a transaction commits, its effects survive subsequent failures. (Recoverability is a schedule property, not one of the four ACID properties.) Hence the property described here is Atomicity.