Discussion
The configuration in which each LED receives operating current of 8 mA from power supply while the port lines sink the current on each port line is :
Answer: B
This is the common anode configuration.
Each LED's anode is tied to the positive supply, through a current-limiting resistor, and its cathode to a microcontroller port pin. When the pin is driven low, current flows from the supply through the LED into the pin, so the port sinks the LED current, about 8 mA here. Microcontrollers such as the 8051 can sink far more current than they can source, because their port outputs are strong only when pulling low, which is why LEDs are wired this way.
In a common cathode connection the cathodes go to ground and the port would have to source the current. 'Driver' and 'buffer' configurations use an external transistor or IC to supply the current, so the port would not be sinking it directly.
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