The radioisotope used in industrial radiography for the rapid checking of faults in welds and casting is

Correct answer: Cobalt-60

Explanation: Industrial radiography needs a strong gamma-ray source to penetrate metal and reveal hidden flaws in welds and castings. Cobalt-60 is a powerful gamma emitter (high energy, good penetration) with a convenient half-life, so it is commonly used for this purpose.

• Carbon-14 — Used mainly for radiocarbon dating, not industrial radiography.
• Phosphorus-32 — Beta emitter; used as a tracer/therapy, poor for thick metal inspection.
• Cobalt-60 — Correct. Strong gamma source for radiography of welds/castings.
• Iodine-131 — Medical (thyroid) applications; not used for checking metal faults.