Classify the following objects into transparent, translucent and opaque objects:
Clean Water, Air, Brown paper, rock, waxed paper, aluminium sheet, thin muslin cloth, clear plastic scale, skin, a CD (compact disc), polythene sheet, dense smoke, heap of salt, glass, milk, carbon paper, spectacles, a wall.

Hint: Go by the definition of transparent, translucent and opaque objects. In a nutshell, transparent objects allow light to pass 100%, translucent allow around 50% to pass while opaque objects do not allow light to pass (0%).

Complete step by step answer:Based on the amount of light allowed to pass through the objects, these are categorized in transparent, translucent and opaque. In terms of optics,
Transparent Objects- Material which does not allow light to scatter and refract comes under this category. If refraction occurs then the refraction is not that prominent.
Translucent objects- Material where light follows Snell’s law and refraction occurs dominantly. Scattering is not prominent but happens. Hence, the objects allow less light to pass and it appears hazy on the other side when looked through these objects.
Opaque objects- Here scattering of light is the most dominant. Therefore, no light is passed and we are not able to see anything on the other side.
Based on the above definitions, we differentiate the given objects into the three categories:
Transparent: Clean Water, Air, glass
Translucent: Waxed paper, thin muslin cloth, clear plastic scale, skin, sheet of polythene, dense smoke, spectacles,
Opaque: Brown paper, rock, aluminium sheet, CD (compact disk), heap of salt, milk, wall, carbon paper.

Note:Try not to get confused in transparent and translucent objects. One trick is to do practical. If the object on the other side appears as it is then the material is transparent like air. On the other-hand if it appears hazy or even a little less clear then translucent like plastic/smoke. These are easily available real-life examples and you can try out.