Answer:
D. Scintillation counter
Explanation:
DNA is usually labelled with radioactive phosphorus, which is a β emitter, so you need a device that can detect β particles.
A scintillation counter detects β particles because they emit a flash of light when they hit a phosphor. The device converts the flashes into electrical signals, amplifies then about a million times, and then counts them.
A, B, and C are wrong. They are all common laboratory equipment, but they can't detect radioactivity of any sort.
