When an n-p-n transistor is used as an amplifier, then:

The correct answer is Option (3) → electron move from base to collector

When an n-p-n transistor works as an amplifier, the emitter-base junction is forward biased and the base-collector junction is reverse biased. The emitter is heavily doped, so the current is carried mainly by electrons.

Option (1) electrons move from collector to base — Incorrect. The reverse-biased collector junction pushes the electrons the other way, from base into the collector.

Option (2) holes move from base to emitter — Incorrect. The base is lightly doped, so the hole flow across the forward-biased junction is only a very small part; the main flow is that of electrons from the emitter.

Option (3) electron move from base to collector — Correct. The base is thin, so only a few electrons recombine there and most of them cross into the collector, which forms the collector current.