Final answer:
The central ray (CR) must be directed perpendicular to the floor to accurately demonstrate undistorted air/fluid levels on an x-ray, ensuring a correct diagnosis.
Step-by-step explanation:
To demonstrate undistorted air/fluid levels on an x-ray, the central ray (CR) must be directed perpendicular to the floor. This positioning ensures that gravity can act on the fluids in a predictable manner, allowing a clear differentiation between air and fluid levels within the body. If the CR is not perpendicular, air-fluid levels could appear tilted or otherwise distorted, which could result in a misdiagnosis.