Final answer:
The correct order of elements in descending size is c) Sodium, potassium, rubidium, and cesium, as elements increase in size down a group due to adding electron shells.
Step-by-step explanation:
To find the group of elements listed in order of decreasing size based on atomic measurements, we look for a group where each subsequent element has a smaller atomic radius. Out of the options provided, the correct answer is:
c) Sodium, potassium, rubidium, caesium
This order reflects the general trend in atomic size for elements within the same group of the periodic table. As we move down a group, atomic size increases. This trend is because each element down a group has an additional electron shell compared to the one before it, making the atom larger. Thus, caesium has a larger atomic size than rubidium, which in turn is larger than potassium, and sodium is the smallest among them. This order is in accordance with elements from Group 1: The Alkali Metals, which include lithium, sodium, potassium, rubidium, caesium, and francium.