Which of the following materials will have the highest attenuation?

Bone has the highest attenuation among the materials listed due to its dense structure and high atomic number. The attenuation of ultrasound waves in a medium is influenced by the material's density and the speed of sound within that material. In general, denser materials and those with higher acoustic impedances lead to greater attenuation.

Bone's high mineral content contributes significantly to its ability to absorb and scatter sound waves, making it much more effective at attenuating ultrasound compared to fat, muscle, and air. While air can also create significant reflection due to its lower density and large acoustic impedance mismatch with soft tissues, bone's overall attenuation is greater because it is solid and denser than both muscle and fat, and it interacts with the ultrasonic waves more intensively.

Fat has the lowest attenuation properties among the soft tissues, allowing more sound to pass through it, while muscle has a moderate level of attenuation. Air, though it can effectively reflect sound, is not considered a solid material like bone, so while it causes significant scattering, it does not generally attenuate in the same way that bone does. This is why bone is recognized for having the highest attenuation in this context.