Final answer:
Potassium (K) has the largest atomic radius among the options given, which are cobalt, nickel, calcium, and potassium. It is positioned in group 1 of the periodic table, where the atomic radius is known to increase as you move down the group.
Step-by-step explanation:
The question is asking to determine which of the given elements has the largest atomic radius: cobalt (Co), nickel (Ni), calcium (Ca), or potassium (K). Atomic radius generally increases down a group on the periodic table and decreases across a period from left to right. Therefore, to find the element with the largest atomic radius, we can look at their positions in the periodic table. Cobalt and nickel are transition metals in period 4, calcium is an alkaline earth metal in period 4, and potassium is an alkali metal in period 4 as well. However, potassium is located in group 1, which is the farthest to the left among the choices. This places it below sodium (Na) and lithium (Li) which are known for their relatively large atomic radii as well. Thus, potassium, being lower in the same group, would have the larger atomic radius compared to cobalt, nickel, and calcium.
K is the element with the largest atomic radius among the options provided. As an alkali metal, potassium's atomic radius is larger than that of calcium, which in turn is larger than those of cobalt and nickel. Among the alkali metals we also find lithium, sodium, rubidium, cesium, and francium - with the atomic radius increasing down the group.