Option 1 states that ultrasonic waves cannot get reflected, refracted, or absorbed. However, this statement is not correct. Ultrasonic waves can indeed be reflected, refracted, and absorbed. When ultrasonic waves encounter a boundary between two mediums, such as air and water, some of the wave is reflected back into the original medium, some is refracted or bent as it enters the second medium, and some is absorbed by the second medium. This phenomenon is similar to how light waves behave when they encounter boundaries. So, option 1 is incorrect.

Option 2 states that ultrasonic waves are used to detect the presence of defects like cracks and porosity in the internal structure of common structural materials. This statement is correct. Ultrasonic testing is a widely used technique in industries to inspect materials for flaws that may not be visible to the naked eye.

Option 3 states that ultrasonic waves can be used for making holes in very hard materials like diamond. This statement is also correct. Ultrasonic machining is a process that uses the mechanical vibration generated by ultrasonic waves to erode or remove material from the surface of hard materials.

Option 4 states that ultrasonic waves cannot travel through a vacuum. This statement is correct. Ultrasonic waves are mechanical waves that require