(solved)Question 3.40 of NCERT Class XI Chemistry Chapter 3

Oxidizing property is directly proportional to the ability to gain electrons.

Florine has the highest oxidizing property because it is the most electronegative element (-4). Hence, the answer is either (a) or (b).

Further, it is known that oxygen is more oxidising than chlorine. In fact, the oxidation state of chlorine in compounds with oxygen and fluorine is always positive. For example, in dichloro heptaoxide ($\displaystyle Cl_2O_7$), chlorine has an oxidation state of +7, with that of oxygen being -2. So we can rule out option (a).

Therefore, option (b) is the right answer F > O > Cl > N

Fluorine is the most electronegative of all the elements of the periodic table, and hence it has the ultimate oxidation power.

Chlorine always has oxidation state of -1 [except in compounds of oxygen (-2) and fluorine (-1)]. So we can conclude that Chlorine has lower oxidation power than oxygen, and from NCl₃ [where the oxidation state of N is +3, chlorine is -1] we can verify that chlorine has greater oxidation power than that of nitrogen.

Based on the above the order is F > O > Cl > N is the answer!