The meaning of the word given below vulnerable means defended. The exact meaning or the reverse of the given word will be the option a pure. Pure means to excuse someone from an obligation. The words vulnerable and pure are synonymous with each other in the given question. thus, the correct option is the optiona. 
The word is given in the option b statutory means needed. The word is given in the option c foe means showing opposition or dislike. 
The word is given in the option d disturbing means fussing. 
The word given in the option e mischance means bad luck. 
Thus, the options b, c, d and e are incorrect as they don't have the analogous or nearly the same meaning of the given word. They've their own particular or specific meaning.