Comprehensive and Detailed Explanation From Exact Extract:
Attenuation increases with both frequency and depth. The highest attenuation occurs at the highest frequency and greatest depth. 7.5 MHz attenuates faster than 5 MHz, and 5 cm represents deeper tissue penetration.
Principles and Instrumentation state:
"Attenuation is directly proportional to frequency and path length: Attenuation = Frequency × Depth × Attenuation Coefficient." Therefore, the correct answer is D: 7.5 MHz at 5 cm.
-

Axial resolution refers to the ability of an ultrasound system to distinguish between two structures that are close to each other along the path of the ultrasound beam. It is primarily determined by the spatial pulse length, which is the product of the wavelength and the number of cycles in a pulse. Shorter wavelengths result in shorter spatial pulse lengths, thereby improving axial resolution. This is because shorter wavelengths (which correspond to higher frequencies) allow for better differentiation between closely spaced structures along the beam's axis.
American Registry for Diagnostic Medical Sonography (ARDMS). Sonography Principles and Instrumentation (SPI) Examination Review Guide.

Color flash artifact occurs due to tissue motion. This artifact is a type of color Doppler artifact that happens when there is movement of tissue or transducer, which causes the Doppler system to incorrectly interpret the motion as blood flow. This results in a flash of color appearing on the image where there is actually no flow.
Tissue motion affects the Doppler signal, leading to misinterpretation by the system, and hence the artifact appears as a flash of color.
References
* ARDMS Sonography Principles and Instrumentation (SPI) Exam Study Guide
* "Diagnostic Ultrasound: Principles and Instruments" by Frederick W. Kremkau

Spectral Doppler mirroring, also known as crosstalk, occurs when the Doppler signal appears on both sides of the baseline. This can be caused by excessively high Doppler gain, which amplifies the signal and creates artificial mirror images. Decreasing the Doppler gain reduces the signal amplitude, thereby minimizing the mirroring artifact.
ARDMS Sonography Principles and Instrumentation guidelines
Hoskins, P. R., Thrush, A., Martin, K., & Whittingham, T. A. (2010). Diagnostic Ultrasound: Physics and Equipment.

Comprehensive and Detailed Explanation From Exact Extract:
Mechanical Index (MI) estimates the likelihood of non-thermal bioeffects such as cavitation (formation of microbubbles).
Principles and Instrumentation state:
"Mechanical Index reflects the risk of cavitation. Higher MI values increase cavitation potential."
* Attenuation coefficient (A) refers to energy loss.
* Thermal index (C) reflects potential heating.
* Frame rate (D) relates to temporal resolution.
Therefore, the correct answer is B: Mechanical index.