Answer:
The average diameter of a helium atom is smaller.
Step-by-step explanation:
Step 1: Data given
An atom gets larger as the number of electronic shells increase; therefore 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 the right of a certain period.
Step 2:
Since hydrogen is more left on the periodic table than helium, the diameter of the atom will decrease moving from hydrogen to helium.
Hydrogen has a bigger diameter than helium.
The average diameter of a helium atom is smaller.