Where will the density of eddy currents be the greatest when a rod is placed in an encircling type of coil?

When a conductive rod is placed within an encircling type of coil, the eddy currents induced within the rod will be most concentrated at its surface. This phenomenon occurs due to the way electromagnetic induction operates.

When an alternating current passes through the coil, it creates a changing magnetic field. This changing magnetic field induces currents in the conductive material of the rod. According to Lenz's law, these eddy currents flow in such a way as to oppose the change that created them. As a result, the induced odes of the magnetic field are greatest at the surface of the rod and diminish with depth into the material.

The skin effect is particularly relevant here, whereby high-frequency currents tend to flow near the surface of conductors rather than uniformly throughout the entire cross-section. This means that the density of the eddy currents will diminish as you move towards the center of the rod. Hence, the correct statement is that the density of eddy currents will be greatest at the surface of the rod.