1st rib is an atypical rib and does not artriculate at 3 sites with a vertebra. It has 2 articulations as follows
Circular facet on the head of the rib with the body of the first thoracic vertebra
tubercle of the rib to the transverse process of the corresponding vertebra
Even though 2nd rib is atypical it articulates with the vertebrae at 3 different sites hence it is not the right answer. Thank you.