Explanation:

- Option 1: Gracilaria

- Gracilaria is a type of red algae.

- It is widely used to produce agar, a gelatinous substance.

- Agar is used in microbiological cultures and as a thickening agent in food.

- Correct Answer

- Option 2: Chlorella

- Chlorella is a type of green algae.

- It is primarily used as a nutritional supplement.

- It does not produce agar.

- Option 3: Sargassum

- Sargassum is a brown algae.

- It is known for its floating mats in the ocean.

- It does not produce agar.

- Option 4: Align

- The word "Align" seems to be a typographical error or unrelated.

- Possibly intended to refer to "Algin," derived from brown algae but not related to agar production.