Question

list the following atoms in order of increasing size (atomic radius): o, cl, se
answer:
cl < o < se
se < cl < o
o < se < cl
o < cl < se

Explanation:

Atomic radius increases down a group (due to more electron shells) and decreases across a period (due to increased nuclear charge attracting electrons closer). O is in period 2, Cl in period 3, and Se in period 4. So O (smallest as it's highest up) < Cl (middle) < Se (largest as it's lowest in the groups considered).

Answer:

D. \(O < Cl < Se\)