Describe what was expected for scattering of alpha particles on the Thomson model. Describe how only a nucleus-electron cloud picture of a small positively charged massive nucleus can account for the observation that some alpha particles were scattered back towards the source. Mention the positive-positive repulsive force. There are three technical reasons. Each of these is roughly equivalent to saying 'mirrors cost less than lenses' but we were calling for the technical reasons behind the dollars.
Lenses suffer from chromatic aberration.
Your answer must explain what this aberration is AND why mirrors are not similarly affected. Mirrors are more easily supported than lenses. A mirror, on the other hand, can be supported over its entire rear surface. Thin mirrors can be made and supported if necessary under computer control, in order to maintain the desired surface shape. In the case of a mirror, the light does not enter the glass.