Which of the following is an example of a constructive force? a. buildings collapse in an earthquake b. river erosion within the grand canyon's rock walls c. weathering of a mountain due to rain d. a volcano eruption i need quickly

 D.a volcano eruption since the lava hardens and forms land
 

Atoms are the smallest unit of matter that can't be broken down chemically. Molecules are groups of two or more atoms that are chemically bonded. Ions are atoms or molecules that have gained or lost one or more of their valence electrons and therefore have a net positive or negative charge.