- Acid can cause rocks to weather by chemical reaction
- Chemical weathering means chemical reaction causes the weathering of rocks
- Hence, acid weathering rocks is a kind of chemical weathering

- Acid weathering rocks is a kind of chemical weathering
- Lichens can produce acid to break down rocks
- Therefore, lichens producing acid to break down rocks is an example of chemical weathering

So, lichens producing acid to break down rocks is an example of chemical weathering
A scientist was examining a large boulder that was covered with lichens (a combination of fungi and algae). He chipped a piece of the rock and placed it under a microscope. He observed that the surface of the rock was breaking down underneath the lichen. Which was the scientist most likely observing?
- Acid can cause rocks to weather by chemical reaction 
- Lichens can produce acid to break down rocks 
- Chemical weathering means chemical reaction causes the weathering of rocks