All Points: 2 Marks
To see any non-luminous object, we need the following:

1) Source of light

2) An object

3) Eyes

When light emitted from a luminous object falls on a non-luminous object and is reflected, the reflected light reaches our eyes and enables us to see that object.

Shadow: 2 Marks
When light falls on an opaque object, a dark patch is formed on the other side of the object, if a screen is present on the other side. This dark patch is known as the shadow.
Eg: 

The image formed by a pin-hole camera is inverted.

Luminous: 1 Mark
Non-luminous: 1 Mark
Examples: 1 Mark
Luminous objects are which emit light by their own.
Examples: - Sun, flame of a burning candle
Non-luminous objects are which can not emit light on their own. These objects reflect light from luminous bodies
Examples: - Moon, Earth

Explanation: 1 Mark each
Examples: 2 Marks
1. When an object does not let light pass through it, the object is known as opaque. We cannot see through them. Example: Wall.
2. If you are able to see clearly through an object, it is allowing the light to pass through it and is transparent. Example: Air, glass.
3. There are some objects through which we can see, but not very clearly. Such objects are known as translucent. Example: Wet glass.

Shadow Formation: 2 Marks
Types of shadows: 2 Marks
Types of Objects: 1 Mark
A shadow is just a space or region where there is no light since an opaque object is blocking light rays. The position and intensity of the source of light affects the properties of the type of shadow that is formed.
Light sources can be either point or non-point (extended) in nature. If it is a point source of light, then it forms a simple shadow called an umbra. If it is an extended light source, the shadow is divided into the umbra, penumbra, and antumbra. They can also be used to define levels of darkness, as is sometimes done when dealing with sunspots.

No, only opaque objects can cast a shadow.

Each Point: 1 Mark
Opaque: a piece of rock, a sheet of aluminum, a mirror, a wooden board, a CD, an umbrella, a wall, a sheet of carbon paper, a sheet of cardboard.
 

Transparent: Air, water, a sheet of plane glass, a sheet of cellophane.

Translucent: smoke, fog, a wire mesh.
 

Luminous: a piece of red-hot iron, a lighted fluorescent tube, the flame of a gas burner, a lighted torch, kerosene stove, Sun, firefly.
 

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, an umbrella, a wall, a sheet of carbon paper, a sheet of cardboard, a sheet of cellophane, a wire mesh, moon.

Opaque objects don't allow the light to pass through them. Mirror doesn't allow light to pass through it. A beam of light gets reflected back after striking the mirror.