The  symbiotic association between algae and fungi is known as :

Lichens

The correct answer is Option (3) –Lichens

Lichens are composite organisms formed by the symbiotic relationship between a fungus (the mycobiont) and a photosynthetic partner, usually green algae or cyanobacteria (the photobiont). The fungal component provides the structural support and protection, while the photosynthetic partner produces organic compounds through photosynthesis, which benefits both organisms.

The other options are:

1. Commensalism: Commensalism refers to a symbiotic relationship where one organism benefits while the other is neither harmed nor helped.
2. Mycorrhiza: Mycorrhiza is a symbiotic association between fungi and the roots of plants. While it involves fungi, it doesn't necessarily involve algae. Mycorrhizal fungi help plants in nutrient uptake, especially phosphorus, in exchange for carbohydrates produced by the plant through photosynthesis.
3. Saprotrophs: Saprotrophs are organisms that obtain nutrients by decomposing dead organic matter. They are not involved in symbiotic relationships like lichens.