37. LED Selection & Failure

Question.9

A product returns from the field with a non-working 5 mm indicator LED.
The LED was driven correctly at 10 mA, and the resistor value is verified.
There are no visible burn marks, but the LED is completely dead.
What is the most likely cause?

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The resistor slowly failed
The LED exceeded forward current rating
Electrostatic discharge (ESD) damaged the LED junction
The LED has lower lifespan