A banking app transfers £500 from Account A to Account B. If the system crashes after debiting Account A but before crediting Account B, the transaction is rolled back so neither account changes.

Which ACID property is demonstrated?

A customer places an online order and receives confirmation. The system crashes immediately after, but when it restarts, the order still exists.
Which ACID property guarantees this?

Transaction A runs a query to count all customers in a loyalty program. While Transaction A is still open, Transaction B adds a new customer and commits. Transaction A runs the same query again and gets a different count.
Which ACID property is violated here?

A database enforces that the sum of all account balances equals £1,000,000. After transferring £100 from Account X to Account Y, the total remains £1,000,000.
Which ACID property ensures this?

Transaction A updates a product price from £50 to £60 but hasn’t committed yet. Transaction B reads the new price (£60) and uses it in a calculation. Later, Transaction A rolls back its change.
Which ACID property is violated here?