The correct answer is option 2: 200 m. In the sea, plants are restricted to a certain depth due to various factors such as sunlight penetration and nutrient availability. Plants require sunlight for photosynthesis, and as the depth of the sea increases, less sunlight reaches the plants. Additionally, nutrient availability tends to decrease with depth, which further limits the growth of plants. As a result, plants are generally found in the upper layers of the sea, up to a depth of around 200 meters. Beyond this depth, the conditions become less favorable for plant growth, and other types of organisms, such as algae and bacteria, become more dominant.