The ocean floor is a flat plain known as the

The correct answer is Abyssal Plain.

Key Points Abyssal plain:

• It is a undulating plain two to three miles below sea level. It occupies two-thirds of the ocean floor and is commonly referred to as the abyssal plain. Hence the correct answer is Option 1.

Additional Information

 Abyssal hills:

• Sea hills on abyssal plains rising less than 1000 meters from the floor are called Abyssal hills.

Oceanic Ridges:

• The oceanic ridge system is a continuous underwater mountain range. It is created when magma rising between diverging plates of the lithosphere cools and forms a new layer of crust.
• Guyots: Guyots are seamounts that have flat tops. All of them are generally of volcanic origin.

Fringing Reef: 

• A fringing reef is one of the three main types of coral reef.
• It grow directly from a shore. 
• They are located very close to land, and often form a shallow lagoon between the beach and the main body of the reef.

​Barrier Reef:

• Barrier reefs are extensive linear reef complexes that parallel a shore, and are separated from it by lagoon.
• This is the largest (in size, not distribution) of the three reefs, runs for hundreds of kilometres and is several kilometres wide.