Lichens, a combination of fungi and algae, grow on the surface of rocks. They secrete acids that slowly eat away at the surface of the rock. Is this an example of chemical or physical weathering?

physical

chemical

Which statement is true about a catalyst? a: a catalyst decreases the rate of the reaction. b. a catalyst is consumed during a chemical reaction. c. a catalyst lowers the activation energy of a reaction. d. a catalyst increases the reactant concentration during a reaction.