The correct answer is: B. Pull down
A depletion-mode MOSFET is a type of MOSFET that is turned on when there is no gate voltage applied. This is in contrast to an enhancement-mode MOSFET, which is turned off when there is no gate voltage applied.
In an nMOS inverter configuration, the depletion-mode MOSFET is used as the pull-down device. This means that it is used to provide a low output voltage when the input voltage is high.
The pull-down device is important because it ensures that the output voltage is always within the desired range. Without a pull-down device, the output voltage could float to an arbitrary value, which could damage the circuit.
The pull-up device is used to provide a high output voltage when the input voltage is low. In an nMOS inverter configuration, the pull-up device is an enhancement-mode MOSFET.
The pull-up device is not as important as the pull-down device because the output voltage is always guaranteed to be high when the input voltage is low. However, the pull-up device can help to improve the speed of the circuit.
The answer to the question “In nMOS inverter configuration depletion mode device is called as . . . . . . . . ” is B. Pull down.