El-Nino develops in the

Pacific ocean
Indian ocean
Mediterranean ocean
Atlantic ocean

The correct answer is (a) Pacific Ocean.

El Niño–Southern Oscillation (ENSO) is a climate pattern that occurs across the tropical Pacific Ocean every few years. During an El Niño event, sea surface temperatures in the eastern tropical Pacific Ocean become warmer than usual. This can lead to changes in weather patterns around the world, including changes in rainfall, temperature, and sea level.

The Indian Ocean, Mediterranean Sea, and Atlantic Ocean do not play a significant role in ENSO.