Asubstance made of two or more elements chemically combined in a set ratio or proportion is called what?

Jewelweed, a flowering plant, has seed pods that burst open when touched and forcefully eject their seeds. these structures are favorable because they a. can cause genetic changes to occur. b. prevent germination within the seed pod. c. aid in the dispersal of the species. d. attract insects that aid in pollination.

The molecular formula for caffeine is cshion402. which of the following elements is not found in caffeine?

Which is the layer underground where all empty spaces are filled with a combination of air and water ?