Which of these statements describes the size of an atom?
a. an atom is larger than a sheet of aluminum foil.
b. an atom is small but can be seen with just our eyes.
c. an atom is the size of a plastic building block.
d. an atom is tiny and cannot be seen without magnification.

D

Explanation:

essentially an atom means "undividable particle" so basically to get an atom out of any element you get to divide it until you can't do it anymore and so you won't see the particle.

the mantle

explanation:

earth is divided into three layers: the crust or the outermost layer on which we live; the underlying, middle layer - the mantle - and the core (the innermost layer of earth).