Q. Which of the following statements regarding lichens are correct:

1. They are a symbiotic association of algae and fungi
2. They serve as indicators of air pollution
3. They can survive in extreme environmental conditions

Select the correct answer using the codes given below:
Answer: 1, 2 and 3
Notes: Lichens are mutualistic partnerships of algae and fungi, act as sensitive bioindicators of air pollution (notably SO₂), and are highly resilient, thriving in extreme conditions like arctic tundra and deserts. Thus, all three statements are correct based on established scientific facts about lichens.