Odisha state Government's tourism webpage says verbatim that Chandipur beach has a unique distinction on its own. Unlike other beaches, the sea water here recedes away from the shore line about five km twice a day, an unusual phenomenon, rarely found anywhere. Therefore answer is "C". Yes, some candidates have been circulating youtube clips of Bhavnagar beach with similar phenomenon, but when it comes to UPSC Answerkey, Government site wins over YouTube or Personal travel diary blogs.