Scientists divide earth into three main layers: the core, the mantle, and the crust. how are these three layers identified?

by their chemical composition

by their structural features

by their plate tectonics

by their physical properties

Hydrogen has only one electron in its only (and outer) electron shell. if a hydrogen atom were to absorb a small amount of energy, where would bohr say the electron would go? a. fly off the atom b. nowhere, it would just speed up. c. spiral inwards towards the nucleus d. move up to another shell that would form