Explanation:

Here’s what’s going on with each option:

- Sargassum is a brown alga, and it’s definitely marine. You’ll find big floating mats out in the Atlantic.

- Porphyra is a red alga, and yes, also marine. It’s the seaweed you see in sushi (nori).

- Chlorella is a green alga. Here’s the thing: Chlorella is found in freshwater environments, not marine. People even use it in freshwater aquariums.

- Laminaria is another brown alga, and again, it lives in the ocean. It’s known as kelp.

So the correct answer really is:

Option 3 – Chlorella is not a marine alga.