Which one of the following is NOT a part of the ACID properties of database…

Concept — A transaction is one logical unit of work on a database, and the guarantees a DBMS must provide for every such unit are summarised by the four-letter acronym ACID. Each letter names a property of how a transaction executes, not a way of describing the data that happens to be stored.

Applying it here — the four letters expand as follows:

• A — Atomicity: the unit of work is indivisible; either all of its operations take effect or none of them do, with partial work rolled back.

• C — Consistency: the unit of work carries the database from one valid state to another, leaving every declared constraint, key and trigger rule satisfied.

• I — Isolation: concurrently running units of work do not observe one another’s intermediate states; the overall effect matches some serial order of execution.

• D — Durability: once a commit returns, the effects survive a later crash or power loss because they are already in stable storage.

Matching the options — Atomicity, Consistency and Durability are three of those four letters. The fourth letter, Isolation, does not appear among the options at all; the term standing in its place is Instance, which belongs to a different part of DBMS vocabulary. An instance is the data actually held in the database at a given moment — the current contents whose structure the schema defines — and it changes with every insert, update and delete.

Cross-check — read each term into the sentence “the DBMS must guarantee ___ for every transaction”. Atomicity, consistency and durability read as transaction guarantees. Instance does not: a database has an instance at all times, whether or not any transaction is running, so it is a description of state rather than a guarantee about execution.

Hence the term that is not part of the ACID properties is Instance.