Consider the following transaction involving two bank accounts x and y.…

Answer: Consistency

Why: Consistency is the ACID property that requires transactions to preserve database integrity constraints. The requirement that the sum of accounts x and y remains constant is an integrity constraint, so ensuring this constraint holds before and after the transaction is a consistency concern.

• The given transaction subtracts 50 from x and adds 50 to y, so if x + y was constant before execution, it remains constant after (x - 50) + (y + 50) = x + y.

• Related ACID roles: atomicity ensures the transfer isn't partially applied; isolation handles concurrent interactions; durability ensures committed changes persist — but the invariant itself is a consistency requirement.