Final answer:
Silicon (Si) has the largest atomic radius among the provided options because atomic radius increases down a group and decreases across a period due to the increase of electron shells. Since Si is the farthest left element in the same period, it has more electron shells and thus a larger radius than P, S, or Cl.
Step-by-step explanation:
To determine which of the options provided has the largest atomic radius, we must consider the elements' positions on the periodic table. Atomic radius generally increases down a group and decreases across a period, primarily due to the increase of electron shells as one moves down a group and an increase in nuclear charge as one moves across a period which draws the electrons closer to the nucleus.
Si (Silicon) is in the third period and the group 14 of the periodic table, P (Phosphorus) is in the same period but in the group 15, S (Sulfur) is also in period 3 but in group 16, and Cl (Chlorine) is in group 17 of the same period. Since all these elements belong to the same period but different groups, their atomic radii decrease from left to right across the period due to increasing nuclear charge. This makes Si the element with the largest atomic radius since it has a greater number of electron shells compared to the others in its period, a more significant factor than nuclear charge when elements are in the same period.
Therefore, the correct answer is Si - Higher atomic number, which in this context refers to the additional electron shell that Silicon has when compared to other elements in the same period.