Question

Which of the following element has the smallest atomic radius?

• A. $K$
• B. $Ca$
• C. $Br$
• D. $Kr$
• E. $Zn$

Answer 1

Answer: (D)

$Kr$

As you go across a period, electrons are added to the same energy level. At the same time, protons are being added to the nucleus. The concentration of more protons in the nucleus creates a higher effective nuclear charge, In other words, there is a stronger force of attraction pulling the electrons closer to the nucleus resulting in a smaller atomic radius. So, all these elements belong to the $4th$ group and Kr has the smallest atomic radii as it lies across the period.