How do waves interact with objects and other waves

What is the ph of a solution that has a hydrogen ion concentration of 1.0 * 10 -9 m?

Scientists discovered fossils in several layers of the earth you see here. they found fossils of algae, snails, and clams in layer d. given that information, where do you think they found fossil evidence of simple land plants and amphibians?

Assume that 13.5 g solid aluminum (al) react with hcl to produce solid aluminum chloride (alcl3) salt and gaseous hydrogen (h2) at standard temperature and pressure.