El Nino develops in which of these oceans?

Correct option is D

El-Nino develops in the Pacific Ocean. El Niño is a climate pattern that describes the unusual warming of surface waters in the eastern tropical Pacific Ocean.
El Nino is associated with a band of warm ocean water that develops in the central and east-central equatorial Pacific (approximately between the International Date Line and 120°W), including the area off the Pacific coast of South America. 
El Niño is accompanied by high air pressure in the western Pacific and low air pressure in the eastern Pacific.