Which of the following elements has the smallest atomic radius
a. carbon
b. lithium
c. potassium
d. bromine

Element with the smallest radius is Carbon.

Explanation:

In a periodic table, atomic radius increases down the group due to addition of a new shell and decreases across the period from left to right due to increasing nuclear charge.

Due to addition of more electrons in same shell and increase of positive charge in nucleus increases attractive forces between electrons and nucleus hence decreasing size.

Carbon and Lithium are present in same period and hence Carbon has smaller size; Potassium and Bromine are present in same period and hence out of the two, Bromine has smaller size.

On comparing Carbon and Bromine, atomic radius increases down the group hence, Carbon has the smallest radius among the four given elements.