1. the tendency of an element to react is closely related to (1 point). a. its atomic mass.. attractions between its atoms.. b. the number of valence electrons in atoms of the element.. c. the ratio of protons to neutrons in atoms of the element.

"the periodic table is arranged in order of atomic number."

indicate valleys, hills, steepness and gentleness of slopes.

explanation:

contour lines on a map indicate elevation, or depth. numeric notations on contour lines refer to the level of elevation, or height about sea level.