Answer and Explanation:
The correct answer is B. The atomic radius increases from left to right across the periodic table.
There are a few factors that contribute to this trend. As you move from left to right across a period (horizontal row), the atomic number increases, meaning there are more protons in the nucleus. The increase in positive charge in the nucleus exerts a stronger pull on the electrons present in the same energy level, causing the electron cloud to be pulled closer to the nucleus.
Additionally, as you move from left to right across a period, the number of energy levels or shells remains mostly constant, while the number of protons and electrons increases. The increase in electron-electron repulsion forces the electrons to spread out over the same energy levels, thus increasing the size of the electron cloud and atomic radius.
However, it is important to note that when moving down a group (vertical column), the atomic radius generally increases. This is because each subsequent row adds a new energy level or shell, increasing the average distance between the nucleus and the outermost electrons. The additional energy levels contribute to shielding the outer electrons from the pull of the nucleus, leading to a larger atomic radius.
So, the atomic radius trend in the periodic table is that it generally increases from left to right across a period and increases from top to bottom within a group.