In a common emitter amplifier circuit using an n-p-n transistor, the phase difference between the input and the output voltages will be

135°

180°

45°

90°

Answer

180°

In common emitter amplifier circuit input and output voltage are out of phase. When the input voltage is increased then i_b is increased, i_c also increases so the voltage drop across R_c is increased. However, increase in voltage across R_C is in opposite sense.