Final answer:
The element in group 6A (16) with the smallest atomic size is Oxygen (O), as the atomic size decreases when moving from left to right across a period and increases when moving down a group.
Step-by-step explanation:
The student asked which element in group 6A (16) has the smallest atomic size, given the options: A) O (Oxygen), B) S (Sulfur), C) Se (Selenium), D) Te (Tellurium). To answer this, we can use the periodic trends regarding atomic radius. As we move across a period from left to right in the periodic table, atomic size decreases. This is because the number of protons in the nucleus increases, which leads to a stronger attraction between the nucleus and the electron clouds, pulling them closer and reducing the atomic size.
However, as we move down a group in the periodic table, the atomic size increases. This is due to the addition of electron shells, which increases the distance between the nucleus and the outermost electrons, thereby increasing the atomic size.
In group 6A (16), as we go from Oxygen (O) at the top to Tellurium (Te) at the bottom, we are moving down the group, and thus the atomic size increases. Therefore, the element with the smallest atomic size in this group is Oxygen (O).