Answer:
1. atomic weight
the average relative mass of each element
2. isotope
one or two or more atoms of the same element with different masses due to different numbers of neutrons
3. period
a horizontal row on the periodic table
4. periodic
something that repeats itself on a regular, predictable basis
3.
I took this last year so yea
It's humans are at top of the evolutionary ladder because they have largest brains.