For each resisters, I chose the value of 1k ohm. Because the Volt from each Pin is 5V and the red LED is 1.8 V drop.
Therefore,
By using Ohm's Law V = I * R: R = 3.2/0.02 which is 160 ohm. That is why I chose 1k resistor (if the ohms is higher than resistor then it will over burden the LED. If the resistor is too high then the flow of electricity is too low).
Three power lines are connected to three pin modes (#13, 12, and 9) and one ground line is connected on the Arduino. Three red LEDs are connected on the Breadboard with three resisters
Three outputs from the Arduino board pin modes (#13, 12, and 9). Then, three red LEDs turn on and off in every 2 seconds simultaneously.
Each red LEDs blink simultaneously every two seconds.
Thank you and have a nice day!