The oxidizing character of elements increases from left to right across a period. Thus, we get the decreasing order of oxidizing property as F > O > N. Again, the oxidizing character of elements decreases down a group. Thus, we get F > Cl. However, the oxidizing character of O is more than that of Cl i.e., O > Cl. Hence, the correct order of chemical reactivity of F, Cl, O, and N in terms of their oxidizing property is F > O > Cl > N.

Therefore, the correct option is - (b) F > O > Cl > N