Explanation:

- Section 52 of the Transfer of Property Act, 1882, deals with the doctrine of lis pendens, which means "pending litigation."

- This doctrine prevents parties in a legal dispute over property from transferring or dealing with the property to defeat the purpose of the litigation.

- Option 1: bona fide purchase: While this section may affect bona fide purchasers, the principle is not about protecting them. It is about ensuring the court's decision is meaningful.

- Option 2: Public policy: The doctrine serves public policy. It stops parties from frustrating the outcome of legal proceedings, ensuring justice is not defeated by changing the property’s ownership during the suit.

- Option 3: Auction sale: Lis pendens applies to all forms of transfer, including auction sales, but it’s not specifically about them.

- Option 4: None of the above: Not correct, as the doctrine upholds public policy.

Correct Answer: Option 2 - Public policy.