Final answer:
Hydrogen (H) has the smallest atomic radius among the list of elements, due to having only one proton and one electron, resulting in a minimal distance between the nucleus and its electron.
Step-by-step explanation:
The student's question requires an understanding of atomic radius trends on the periodic table. Among the elements listed (H, Zn, K, Li), hydrogen (H) has the smallest atomic radius due to its position in the periodic table. Hydrogen only has one proton and one electron, which means its electron is close to the nucleus and not shielded by any other electrons, leading to a smaller atomic radius. As we move from left to right across a period on the periodic table, atomic radius decreases due to an increase in the number of protons and a corresponding increase in the effective nuclear charge, drawing the electrons closer to the nucleus. Therefore, among the given options, hydrogen has the smallest atomic radius, making option A) H the correct choice.