<p>Remember, atomic radii decrease moving across a period from left to right. This is because protons are added to the nucleus and these protons attract the electrons more strongly, pulling them in tighter and decreasing the atomic radius. Atomic radius increases moving down a group or family, however, because the value of n increases as you add another shell, the electrons spend more time away from the nucleus, dissipating the attraction between nuclear protons and themselves. Since fluorine and chlorine are both in the same group but chlorine is below fluorine, we know that chlorine is bigger than fluorine. Sulfur is to the left of both chlorine and fluorine, so it must be the smallest of all. Arranged in order of increasing size, they are S, F, Cl, or answer E.</p>
<p>My answer is F CL S</p>