Why you use mirrors as reflectors and not alluminium?
Nearly all modern mirrors are aluminum. An aluminum coating is placed on a sheet of polished glass. In common mirrors we observe this aluminum reflector through the glass layer. But if we turn the mirror around, we can bounce light directly off the aluminum, and this is called a "front surface mirror." (Common mirrors have a coating of hard paint over the thin delicate aluminum coating to prevent scratches.) It's perfectly possible to form a mirror by grinding and polishing a thick aluminum slab. But aluminum is softer than glass, and would collect scratches and dings. Also, aluminum is expensive, so an aluminum mirror costing several dollars might replace a glass mirror costing a few cents.
There are two basic optical designs-- Refractors, which use solid glass lenses to focus the light, Reflectors, which use (mainly) reflecting mirrors to focus light. Many design variables determine whether refractors or reflectors are the best choice, but for very big astronomical telescopes, reflectors are always much cheaper.
Mirrors are used for different purposes.Common ones are- As mirrors at home for seeing your reflection As side mirrors in cars In street light reflectors In medical profession.For e.g. a dentist uses a mirror to spot cavities in your teeth. As a surface for reflecting back laser beams As the inside of a kaleidoscope
Large lenses deform under their own weight, but mirrors can be supported. Reflectors do not suffer from chromatic aberration like refractors do. Large mirrors need only one optical surface, achromats four surfaces to grind. Large, very clear lenses are harder to cast than more tolerant mirror blanks.
To view physical appearance by own-self. answer #2 grocery store scanners use mirrors to direct the lasers, many other laser applications use mirrors to move and direct the beams. Many industrial processes use mirrors and lasers to direct light and laser beams. You use mirrors to drive safely. Warehouses use mirrors on the corners to prevent collisions. Many camera have mirrors in them. We use mirrors for many different applications.