Change into passive voice:
The detective found the lost necklace.

Rules of Conversion from Active to Passive Voice:
1. Identify the subject, the verb and the object: S+V+O
2. Change the object into subject
3. Add suitable helping verb or auxiliary verb according to the tense present in the sentence.
4. Change the verb into past participle of the verb
5. Add the preposition "by“
6. Change the subject into object

Example: Active Voice: Sameer wrote a letter. (Subject) + (verb) + (object).
Passive Voice: A letter was written by Sameer. (Object) + (auxiliary verb) + (past participle) + (by subject).

Option 2 follows all the required rules of sentence transformation.