Step 1: Frame the relationship.
We need the name of the partnership between fungi and algae living together.
Step 2: Role of the alga.
The algal partner has chlorophyll and makes food by photosynthesis for both.
Step 3: Role of the fungus.
The fungal partner absorbs water and minerals and gives shelter and protection.
Step 4: Name the association.
This stable mutual partnership of fungi and algae is called a lichen.
Step 5: Reject the distractors.
Chrysophytes are protists, sponges are animals, and mycorrhiza is fungus plus plant roots, not algae.
Step 6: Conclude.
So the correct term is lichens, which is option 2.
\[ \boxed{\text{Lichens}} \]