Some reptiles, like snakes, have olfactory receptors (smell)

on their tongues
on the roof of their mouths
on their skin
at the tip of their tails

I think the correct answer would be the second option. Some reptiles, like snakes, have olfactory receptors (smell) on the roof of their mouths. As we can observe, snakes usually flick their tongues. This action is made so that they would collect substances from the ground or the air. Their tounges do not have the receptors for smell and taste rather it is located in the roof of the mouth or the vomeronasal. As the tongue goes inside the mouth of the snake, it is being received by the receptors in the mouth and would transmit a number of signals to the brain. The tongue simply deposit the substances that was collected onto the mouth.