Which pin has a built-in LED on many Arduino boards?

• A. Pin 7
• B. Pin 10
• C. Pin 8
• D. Pin 13

Answer: (D)

A built-in LED is provided on many Arduino boards by wiring a small LED to one of the digital I/O pins through a resistor. This gives you an immediate visual indicator of the pin’s state without needing any extra components. When you set that pin HIGH in your code, current flows through the LED and it lights; when you set it LOW, it turns off. This makes it easy to test and learn digital output right away, using a simple blink program. The LED is placed to support quick verification—often it’s the same pin targeted by the standard blink example—so you can see activity as soon as the sketch runs. If you need the exact pin for your specific board, check the board’s schematic or documentation.