* Atomic Size Trends: Atomic radius generally increases as you move down a group (column) on the periodic table and decreases as you move across a period (row) from left to right.

* Location on the Periodic Table:

* Hydrogen (H) is in the first period and group 1.

* Sodium (Na) is in the third period and group 1.

* Lithium (Li) is in the second period and group 1.

Explanation:

* Hydrogen is the smallest because it's in the first period.

* Lithium is smaller than sodium because it's higher up in the same group (group 1).

Therefore, hydrogen (H) has the smallest atomic radius out of hydrogen, sodium, and lithium.