The contents of an EPROM chip are erased by exposing it to

The correct answer is B, ultraviolet light. An Erasable Programmable Read Only Memory chip carries a small quartz window over the silicon; ultraviolet light shone through that window releases the trapped charge from every cell at once and returns the chip to its blank state, after which it can be programmed again.

Option A, an electrical signal, erases EEPROM, the electrically erasable version, and this is the single most common confusion in the chapter: EPROM needs light, EEPROM needs a voltage, and EEPROM can be erased one byte at a time without removing the chip. Option C, a magnetic field, erases magnetic media such as tape or a floppy disk, not a semiconductor ROM. Option D, infrared radiation, does not carry the energy needed to free the trapped electrons and is only a distractor. Remember also that MROM is written by the maker and PROM can be written once.