Correct : c

The correct answer is Option C — Isolation.
In this scenario, two transactions simultaneously read the same balance of Rs. 11,000 from account A before either of them wrote their update back. Both then proceeded to debit Rs. 10,000 each, but since both read the original value, account A was only debited once (ending at Rs. 1,000 instead of going negative), while account B was credited twice.
This is a classic lost update anomaly — one transaction''s write overwrites the other''s, caused entirely by concurrent access without proper isolation. If isolation had been enforced, the second transaction would have seen the updated balance (Rs. 1,000) after the first committed, and the transfer would have been rejected or the balance correctly updated.
Option A — Atomicity: Not violated. Both transactions completed fully — each read, debited, and credited as intended. Neither was partially executed.
Option B — Consistency: Consistency violations are caused by a single transaction breaking integrity constraints. Here, both individual transactions were internally consistent — the problem arose from their concurrent interaction, which is an isolation issue.
Option D — Durability: Not violated. Both committed changes persisted — in fact, that''s part of the problem. The data was durably stored, just incorrectly due to the isolation failure.
The root cause is clearly Isolation — concurrent transactions were allowed to interfere with each other''s reads and writes.