Cl < Si < Fe < Ca <K
The atomic radius decreases from left to right across a period and increases from top to bottom in a group.
Thus, the largest atoms are at the lower left and the smallest are at the upper right.
Locate the atoms in the Periodic Table (see the attached image).
In decreasing order of size, K > Ca > Fe > Si > Cl.
The order from smallest to largest is Cl < Si < Fe < Ca <K.
