Convert the statement into passive. 

"Neha has purchased a new necklace for her sister."

In the active voice, the subject performs the action. The given statement "Neha has purchased a new necklace for her sister" is in active voice as the subject of the sentence, Neha is the doer of the verb purchased. We need to change this into passive voice. In the passive voice, the subject will be shown as affected by the verb. The tense of the given statement is present perfect. In order to change the active voice which uses has or have and the past participle form of the verb as in the question, we need to use "been" after has or have and then the corresponding verb in the past participle form. Option B and option D can be eliminated based on this. In option C, the meaning of the sentence itself is wrong in comparison to the given statement. The correct usage is seen only in option A and hence it is the right answer.