Final answer:
Atoms can be compared in size based on their position in the periodic table. As you move from left to right across a row, the atoms get smaller.
Step-by-step explanation:
When comparing atoms, their size can be determined based on their position in the periodic table. As you move from left to right across a row, the atoms get smaller. So in Part A, Al is to the left of S, making it larger. In Part B, Ge is to the left of Po, making it larger. In Part C, Cr is to the left of W, making it larger. And in Part D, F is to the right of Se, making F smaller in size.