What do you call the water holding compounds produced in large quantities by marine brown and red algae?

Hydrocolloids

The correct answer is Option (3)- Hydrocolloids

The water-holding compounds produced in large quantities by marine brown and red algae are known as Hydrocolloids. Hydrocolloids are complex polysaccharides that have the ability to form gels or viscous solutions when they come in contact with water. In the context of marine algae, these compounds play a role in providing structural support, storing water, and influencing the physical properties of seaweed. They are also used in various industrial applications, particularly in the food and pharmaceutical industries.