Final answer:
(periodic table) Radii __Decreases_ left to right.
The trend on the periodic table is that atomic radii decrease from left to right across a period due to an increase in nuclear charge which pulls electrons closer, and increase top to bottom down a group due to additional electron shells. The correct answer option 2. Decreases.
Step-by-step explanation:
The question is asking about how the atomic radii trend on the periodic table. The atomic radius is a measure of the size of an atom; generally, the distance from the nucleus to the outer electron shell. Observing the trend across periods (left to right) on the periodic table, we see that atomic radii decrease as the atomic number increases.
This occurs because, across a period, electrons are added to the same energy level but the nucleus gains more protons, creating a stronger pull on the electrons, thus making the atom smaller.
When assessing the trend down a group (top to bottom), the atomic radii increase. This is because each successive element down a group has an additional electron shell, resulting in a larger principal quantum number and a larger valence shell that lies farther away from the nucleus.
Despite some exceptions, such as Polonium (Po), the general trend on the periodic table is that atomic radii decrease across periods and increase down groups.
The correct answer option 2. Decreases.