The correct option is 2 and 3 only.
Explanation
The continental shelf is the extended margin of each continent occupied by relatively shallow seas and gulfs. It represents the submerged edge of the continent connecting the coastline to the deep ocean basin.
- Statement 1 is Incorrect: The continental shelf is the shallowest part of the ocean, not the deepest. It is characterized by a very gentle gradient, typically 1° or even less. A gradient of 2° to 5° is characteristic of the continental slope, which lies beyond the shelf.
- Statement 2 is Correct: The seaward edge of the continental shelf is marked by a distinct and sharp increase in slope. This transition point, where the gentle gradient of the shelf turns into a steep descent, is technically known as the shelf break.
- Statement 3 is Correct: The width of continental shelves varies significantly depending on the tectonic environment. For example, the Siberian Shelf in the Arctic Ocean extends up to 1,500 km in width, whereas the shelves along the coasts of Chile and Sumatra are extremely narrow due to the presence of active subduction zones and deep ocean trenches nearby.
Key Takeaway: The continental shelf is the gently sloping (gradient ≤ 1°), submerged extension of a continent that ends at the shelf break. Its width is highly variable, ranging from negligible in active tectonic margins to hundreds of kilometers in passive margins.