Context

ACID is a core database concept that matters whenever you work with transactional data such as payments, account balances, or statement updates. In analytics and operational systems, understanding ACID helps you reason about correctness when multiple writes happen at the same time.

Question

You are asked to explain the four ACID properties in a relational database. Define Atomicity, Consistency, Isolation, and Durability, and describe what each one guarantees during a transaction. You should also explain why these properties matter in a payment or ledger-style workflow, such as updating balances for an American Express card account.

Scope guidance

Keep your answer at an interview level: give clear definitions, a practical example for each property, and mention at least one common misconception or trade-off, especially around isolation and consistency.