What kind of electromagnetic energy penetrates solids?

Answer 1

All electromagnetic waves technically have the ability to penetrate solids depending on the solid itself. However in a practical sense:-

High energy electromagnetic particles can pass through solids such as X-rays (to some extent) and Gamma rays which can pass through several metres of lead reinforced concrete.

Radio waves and microwaves can also pass through solids hence why we use these frequencies to communicate.

Infra-red can permeate through house walls and such. Hence why infrared cameras are used by police.

visible and ultraviolet will only pass through transparent substances or really thin solids. They are more likely to be absorbed or reflected than to pass through objects.