The correct answer is option-2: cc-Ray.

To understand why cc-Ray is the least penetrating power ray, we need to understand the concept of penetrating power. Penetrating power refers to the ability of a ray to pass through different materials. In this case, we are comparing different types of rays - X-Ray, cc-Ray, 3-Ray, and y-Ray - based on their penetrating power.

X-Rays are known to have a relatively high penetrating power. They can pass through soft tissues but are absorbed by denser materials like bones.

cc-Rays, on the other hand, have a lower penetrating power compared to X-Rays. They can penetrate soft tissues but are also easily absorbed by denser materials.

3-Rays are not a well-known type of ray, so it is difficult to determine their penetrating power. However, based on the given options, it can be assumed that 3-Ray may have a higher penetrating power than cc-Ray.

y-Rays are known to have the highest penetrating power among the given options. They can easily pass through various materials, including thick layers of concrete or lead.

Therefore, based on the given options, cc-Ray is the least penetrating power ray.