Which of the following elements has the smallest atomic radius?

• A. calcium
• B. potassium
• C. titanium
• D. scandium

Answer: (C)

Verified step by step guidance

1. Recall that atomic radius generally decreases from left to right across a period in the periodic table due to increasing nuclear charge pulling electrons closer to the nucleus.
2. Identify the positions of the elements calcium (Ca), potassium (K), titanium (Ti), and scandium (Sc) on the periodic table: potassium and calcium are in period 4, group 1 and 2 respectively; scandium and titanium are transition metals in period 4, groups 3 and 4 respectively.
3. Understand that moving from left to right across period 4, atomic radius decreases because the number of protons increases, which increases the effective nuclear charge, pulling electrons closer without much increase in shielding.
4. Compare the elements: potassium (group 1) has the largest atomic radius, followed by calcium (group 2), then scandium (group 3), and finally titanium (group 4) which has the smallest atomic radius among them.
5. Conclude that titanium has the smallest atomic radius because it is furthest to the right in period 4 among the given elements, resulting in the greatest effective nuclear charge and smallest size.