In Period 4 of the periodic table, the element with the smallest atomic radius, excluding noble gases, is germanium (Ge).
As we move across a period from left to right, the atomic radius generally decreases. This decrease is due to the increase in the positive charge of the nucleus as protons are added, which pulls the electrons closer to the nucleus. In Period 4, the elements start with potassium (K) and go through calcium (Ca), scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), and end with zinc (Zn) before reaching the noble gases starting with krypton (Kr).
Germanium, being located to the right side of the fourth period, experiences a stronger nuclear charge relative to its size compared to the elements to its left, resulting in a smaller atomic radius.