Security question

Is it possible to add security question which user need to answer to complete registration?

You can't really do a question, but you can add image verification. The tutorial is here.

Or he can add a advanced profile field that is to be necessarily filled.
Then they will have to answer the question in order to register.
How ever it will let the registration go through, so he might want to activate the members his self so he can check them first.

Other then that the image verification will work as Harperboy326 has said.