When the input voltage is reduced to zero in a closed loop configuration, the circuit acts as both inverting and non-inverting amplifier characteristics combined. The correct answer is (c) Inverting and non-inverting amplifier.
In a closed-loop op-amp configuration with zero input signal:
- The virtual short concept still applies (input terminals at same potential)
- The feedback network determines the behavior
- The circuit acts based on both the feedback path configuration and the signal routing
- Both inverting and non-inverting properties may be exhibited depending on the complete circuit configuration
This is related to the input offset voltage phenomenon where even with zero input, the circuit may exhibit both types of amplifier characteristics due to the overall feedback network structure.