The correct option is 1 and 3 only.
Explanation
The ocean floor, or abyssal plain, is not a flat, featureless surface. It exhibits complex relief features similar to, and often more dramatic than, those found on the continents. This topography is studied through bathymetry.
Statement-wise Analysis:
- Statement 1 is Correct: Geographically, the world's oceans (Pacific, Atlantic, Indian, Arctic, and Southern) are connected and form a single continuous body of saline water often referred to as the "World Ocean." Unlike continents, which are distinct landmasses, oceans merge naturally, making physical demarcation difficult without arbitrary boundaries.
- Statement 2 is Incorrect: The average depth of the ocean is approximately 3,800 meters. The continental shelves, which are generally shallower than 200 meters (and certainly less than 1 km), constitute only about 7.6% of the total ocean area. The vast majority of the ocean floor lies at depths between 3,000 and 6,000 meters (the deep sea plains).
- Statement 3 is Correct: The ocean floor is extremely rugged and geologically active. It contains the world's longest mountain ranges (Mid-Ocean Ridges), deepest trenches, and largest plains. For example, the Mid-Atlantic Ridge is a submerged mountain range longer than any on land.
Key Takeaway:
The ocean floor is characterized by diverse relief features such as ridges, trenches, and seamounts, with the majority of its area located at depths significantly greater than 1 km.