The trend of atomic radii within a period (row) of the periodic table is generally decreasing from left to right. This is because the number of protons in the nucleus increases from left to right, which leads to a stronger attraction between the positively charged nucleus and the negatively charged electrons. This increased nuclear charge pulls the electrons closer to the nucleus, resulting in a decrease in the atomic radius.

In the case of fluorine, oxygen, and chlorine, all three elements belong to the same period (period 2). Fluorine is on the far left, followed by oxygen, and then chlorine. Therefore, fluorine has the smallest atomic radius compared to oxygen and chlorine due to having the lowest atomic number and the strongest nuclear charge.

Here's a summary of the atomic radii of fluorine, oxygen, and chlorine:

- Fluorine (F): 72 picometers (pm)

- Oxygen (O): 73 pm

- Chlorine (Cl): 99 pm

As you can see, fluorine has the smallest atomic radius among the three elements, consistent with the trend of decreasing atomic radii across a period.