Lichens are an example of -

Mutualism

The correct answer is Option (3) → Mutualism    

Mutualism is an interaction that benefits both species involved. One example of mutualism is the symbiotic relationship between lichens .Lichens consist of a fungus and photosynthetic algae, and they rely on each other for survival. The fungus provides a protected environment and absorbs water and nutrients, while the photosynthetic partner conducts photosynthesis and produces energy-rich carbohydrates that benefit both organisms. Another example is mycorrhizae, where fungi form associations with the roots of higher plants.