Options for each Cell wall
Chloroplast
Cytoplasm
Endoplasmic reticulum
Lysosome

c- cold periods in earth's history during which glaciers covered much of the surface.

explanation:

periodic trends is an atom that gets larger as the number of electronic shells increase, the radius of atoms increases as you go down a certain group in the periodic table of elements. in general, the size of an atom will decrease as you move from left to right of a certain period.

the answer is na (sodium)

where are the choice options?