All of the following uses are practical applications of x-ray except

Analyze the question: We need the one use that is NOT an application of X-rays.

Concept: X-rays are high-energy electromagnetic waves with very short wavelengths. They penetrate soft tissue but are absorbed by dense materials such as bone. This gives them these practical uses:

• Medical imaging: detecting bone fractures, dental X-rays, and checking for foreign objects.
• Radiotherapy: high-energy X-rays destroy cancerous cells in tumors.
• Industrial use: checking for cracks in metals and welds, and airport baggage scanning.
• Crystallography: studying the structure of crystals.

Checking each option:

• A. Treatment of tumors: Yes. This is radiotherapy.
• B. Determining the depth of a mine: No. X-rays can't measure depth underground. Depth is found by methods such as sonar or echo-sounding (using sound waves), ropes and measuring lines, or surveying and seismic techniques.
• C. Dental operation: Yes. Dental X-rays are used to examine teeth and roots.
• D. Detecting fractures in bones: Yes. This is the most common use of X-rays.

Tip: For "all of the following except" questions, check each option against the known uses. X-rays are linked to imaging, medical treatment, and material inspection. Measuring depth or distance usually points to sound (echo) or radar, not X-rays.