Q.No.3 - Write a program to On/Off three led bulb in such way 1- On, 2 & 3-OFF, 2-ON, 1 & 3-OFF with use of resistor(220ohm).

Sol.- 

int red=2;
int green=4;
int blue=7;
void setup()
{
  pinMode(red,OUTPUT);
  pinMode(green,OUTPUT);
  pinMode(blue,OUTPUT);
}
void loop()
{
  digitalWrite(red,1);
  delay(1000);
  digitalWrite(red,0); 
  digitalWrite(green,1);
  delay(1000);
  digitalWrite(green,0);
  digitalWrite(blue,1);
  delay(1000);
  digitalWrite(blue,0);
}




Explain : 
Generally use resistor with led so the led would not burn.
Step 1: In coding we declare three varaiables red,green,blue and assign the value of digital pin which is use in led.
Step 2: void setup () initialize pin.
Step 3: Set loop- in this 1st led on and hold 1sec. then OFF. After that 2nd ON and hold 1 sec. then OFF and so on.

OUTPUT: