int mode = 0;
void setup()
{
  pinMode(10, OUTPUT);
  pinMode(11, OUTPUT);
  pinMode(12, OUTPUT);
  pinMode(13, OUTPUT);
  pinMode(2, INPUT);
  Serial.begin(9600);
}

void loop()
{
  int btnValue = digitalRead(2);

// Detect button press
  if (btnValue == HIGH )
  {
    mode=mode+1;
    if(mode>3)
      mode=1;
	Serial.println("Button Pressed");
    delay(1000);    // Debounce
  }
  Serial.println(mode);
  if(mode==1)
  {
      digitalWrite(10, HIGH);
      digitalWrite(11, HIGH);
      digitalWrite(12, HIGH);
      digitalWrite(13, HIGH);
      delay(1000);

digitalWrite(10, LOW);
      digitalWrite(11, LOW);
      digitalWrite(12, LOW);
      digitalWrite(13, LOW);
      delay(1000);
  }
  else if(mode==2)
  {

// Second Press: Turn OFF all LEDs

digitalWrite(10, LOW);
      digitalWrite(11, LOW);
      digitalWrite(12, LOW);
      digitalWrite(13, LOW);    
    
  }
  else if(mode==3)
  {

// Third Press: Alternate blinking
    
      // Even LEDs (10 & 12)
      digitalWrite(10, HIGH);
      digitalWrite(12, HIGH);
      digitalWrite(11, LOW);
      digitalWrite(13, LOW);
      delay(500);

// Odd LEDs (11 & 13)
      digitalWrite(10, LOW);
      digitalWrite(12, LOW);
      digitalWrite(11, HIGH);
      digitalWrite(13, HIGH);
      delay(500);
  }
 
}

O Level Exam : Practical Question

🖥 Output: