which element has the smallest atomic radius?\no calcium\no potassium\no scandium\no titanium

Brief Explanations:

Atomic radius decreases across a period. Calcium (Ca), potassium (K), scandium (Sc), and titanium (Ti) are in the same period (period 4). As we move from left - to - right across a period, the number of protons increases, pulling the electrons closer to the nucleus, reducing the atomic radius. Potassium is the left - most among them, and titanium is the right - most.

Answer:

D. titanium