Which of these parts of the atom is directly involved in chemical changes?
a. electron
b. nucleus
c. neutron
d. proton

All living organisms are composed of a. at least three cells. b. one or more cells. c. only one cell. d. at least 100 cells.

The tilt of the earth's axis of rotation is responsible for the a) ocean's tides. b) size of the moon. c) brightness of stars. d) earth’s seasons.

Place the elements below in order of decreasing ionization energy. aluminum(al) chlorine(cl) magnesium (mg) sulfur(s)