Final answer:
The atomic radius increases as you move down a group and decreases across a period. Si has a larger atomic radius than S, and Te is larger than S. Rb will have the largest atomic radius compared to Sr, Sn, and In.
Step-by-step explanation:
In chemistry, the size of atoms, or the atomic radius, tends to increase as you move down a group in the periodic table due to additional electron shells. Likewise, atomic radius decreases as you move from left to right across a period because the greater nuclear charge pulls electrons closer. For example, cesium (Cs) has a larger atomic radius compared to other elements such as lithium (Li), rubidium (Rb), nitrogen (N), fluorine (F), and iodine (I) because it is further down the group in the periodic table. Referring to the given choices (a) Si or S, (b) S or Te, the larger atom for a. is Si since it is to the left of S, and for b., the larger atom is Te, as it is below S on the periodic table. In a comparison between Sr, Sn, Rb, and In, element Rb would have the largest atomic radius because it is located further down the group than the others.