Question

Classify the objects or materials given below as opaque, transparent or translucent and luminous or non-luminous.
Air, water, a piece of rock, a sheet of aluminum, a mirror, a wooden board, a sheet of polythene, a CD, smoke, a sheet of plane glass, fog, a piece of red hot iron, an umbrella, a lighted fluorescent tube, a wall, a sheet of carbon paper, the fame of a gas burner, a sheet of cardboard, a lighted torch, a sheet of cellophane, a wire mesh, kerosene stove, sun, firefly, moon.

Answer 1

Hint: Use the concept that opaque is not transparent in this question, translucent is semi-transparent and later use the property in the solution that non-luminous elements don't have their own light they receive light from other sources and shine later, for instance moon.

Complete step by step answer:
 Opaque-Unable to see through that i.e. not transparent.
Transparent-Could have seen through.
Translucent-Transparency is the physical property of allowing light to pass through the material without excessive light dispersion. Translucent material consists of materials of different refractive indices.
On the other hand transparent material is composed of components with a uniform refractive index.
Luminous-Relates to light as perceived by the eye, rather than its actual energy.
Non-luminous-Opposite of luminous.

On the basis of above definitions the classification of given objects is given below:

S.no	Object name	Opaque/transparent/translucent	Luminous/non-luminous
1	Air	Transparent	Non-luminous
2	Water	Translucent	Non-luminous
3	A piece of rock	Opaque	Non-luminous
4	A sheet of aluminum	Opaque	Non-luminous
5	A mirror	Opaque	Non-luminous
6	A wooden board	Opaque	Non-luminous
7	A sheet of polythene	Translucent	Non-luminous
8	A CD	Opaque	Non-luminous
9	Smoke	Translucent	Non-luminous
10	A sheet of plane glass	Transparent	Non-luminous
11	Fog	Translucent	Non-luminous
12	A piece of red hot iron	Opaque	Luminous
13	An umbrella	Opaque	Non-luminous
14	A lightened fluorescent tube	Opaque	Luminous
15	A wall	Opaque	Non-luminous
16	A sheet of carbon paper	Opaque	Non-luminous
17	The fame of a gas burner	Opaque	Luminous
18	A sheet of cardboard	Opaque	Non-luminous
19	A lighted torch	Opaque	Luminous
20	A sheet of cellophane	Transparent	Non-luminous
21	A wire mesh	Opaque	Non-luminous
22	Kerosene stove	Opaque	luminous
23	Sun	Opaque	Luminous
24	Firefly	Opaque	luminous
25	moon	Opaque	Non-luminous

So this is the required answer.
Note – Whenever we face these types of questions, remember all the standard meanings of the given properties and define the given objects according to those properties as above which is the answer needed.