Auroras occur in the
a. troposphere
b. stratosphere
c. mesosphere
d. thermosphere

Auroras occur in the "thermosphere".

The thermosphere lies between the exosphere and the mesosphere.It is a district of expanding temperature in Earth's climate that is situated over the mesosphere.  

The thermosphere significantly helps in ensuring the earth and making space investigation and present day types of correspondence conceivable. It additionally supports and ensures life on the planet. It reuses water, retains the sun's energy, and makes a moderate temperature.  

The aurora (Northern Lights and Southern Lights) generally present in the thermosphere. It is a  natural electrical marvel described by the presence of streamers of rosy or greenish light in the sky, particularly close to the northern or southern attractive shaft. The impact is caused by the communication of charged particles from the sun with iotas in the upper atmosphere.