Which of the following elements has the smallest atomic radius?

helium is the smallest element and francium is the largest

since the atomic number is the number of protons in the nucleus, as we move to the left on the periodic table, the electrostatic pull between the nucleus and the valence electron shell decreases. as we move down a group (vertical column), the valence shell energy level gets further and further from the nucleus.

i believe it is-

d.) gravity pulled particles of dust and gas together to form planets.