The element that has the smallest atomic radius is <u>titanium</u>
<em><u>explanation</u></em>
Calcium,potassium, scandium and titanium are in period 4 in the periodic table.
Generally the atomic radius decreases across the period (from the left to the right) . This is because across the period there is increase in nuclear charge which make electrons been strongly attracted to the nuclear.
Titanium is in atomic number 22 thus it has more nuclear charge that calcium,potassium and scandium therefore titanium has the smallest atomic radius.
It is known that in a periodic table, atomic size decreases when we move from left to right.
The given elements potassium, calcium, scandium, and titanium all belongs to third period.
Therefore, out of these elements potassium is at the extreme left and titanium is towards the right. Thus, we can conclude that titanium is the element which has the smallest atomic radius.
