At sunset or sunrise the suns rays have to pass through a larger distance in the atmosphere and most of the blue and other shorter wavelengths are remove by scattering.

To an astronaut it will appear as black.On earth we see the blue sky due to presence of atmosphere. Atmosphere refracts light ray coming from the sun and we see the colour of sky.In space, due to the absence of the atmosphere the light rays do not refract and reach the astronomer's eyes therefore it appears black.

Answer is D.
We cannot see through fog because of scattering.
Atoms and molecules in the air, including anything carried in the air like dust or smoke, will scatter light. Water droplets, as they are present in fog, also scatter light. The light falling on an object and reflected to a viewer can be scattered to heck and back before it gets to the place where it can be 'seen' by an observer. So the observer just sees a 'whiteout' instead of being able to make out anything beyond a few meters or so.

Answer is A.

Stars, except for the Sun, although they may be millions of miles in diameter, are very far away.  They appear as point sources even when viewed by telescopes.  The planets in our solar system, much smaller than stars, are closer and can be resolved as disks with a little bit of magnification. 
Since the Earth's atmosphere is turbulent, all images viewed up through it tend to 'swim.' The result of this is that sometimes a single point in object space gets mapped to two or more points in image space, and also sometimes a single point in object space does not get mapped into any point in image space.  When a star's single point in object space fails to map to at least one point in image space, the star seems to disappear temporarly.  This does not mean the star's light is lost for that moment.  It just means that it didn't get to your eye, it went somewhere else.
Since planets represent several points in object space, it is highly likely that one or more points in the planet's object space get mapped to a points in image space, and the planet's image never winks out.  Each individual ray is twinkling away as badly as any star, but when all of those individual rays are viewed together, the next effect is averaged out to something considerably steadier.
The result is that stars tend to twinkle, and planets do not.

The higher the wavelength the lesser the scattering. Yellow light has higher wavelength so it is least likely to be scattered among all colours in the visible region (except red & orange). So this light is visible from long distance even when there is foggy weather.

Among the constituent colours of white light, red has the longest wavelength and hence least frequency. As a result, red is least scattered among all colours. So, red colour reaches our eyes while all other colours scatter away during sun-rise and sun-set.

Red light is the least scattered by fine particles, fog or smoke present in the atmosphere which makes it easier to detect any danger clearly and distinctly.

A true solution does not have any fine particles dissolved in it which prevents scattering of light thus making it invisible.

The earths atmosphere is a heterogeneous mixture of minute particles like smoke, tiny water droplets, suspended particles of dust and molecules of air. When a beam of light strikes such fine particles, the path of the beam becomes visible. This phenomenon of scattering of light by the colloidal particles is called Tyndall effect.

The molecules of water and other fine particles in the atmosphere scatter light of shorter wavelengths at the blue end than light of longer wavelengths at the red end. Thus, when sunlight passes through water and air, the fine particles scatter the blue color more strongly than red. This scattered blue light enters our eyes and makes the ocean and sky appear blue. Near the horizon sunlight passes through thicker layers of air having larger particles that scatter light of longer wavelength such as the red end of the spectrum. Also it travels larger distance at horizon causing most of the light of shorter wavelength at the blue end of the spectrum to scatter away by the small particles of the atmosphere before reaching the earth.

Near the horizon sunlight passes through thicker layers of air having larger particles that scatter light of longer wavelength such as the red end of the spectrum. Also it travels larger distance at horizon before reaching the earth. However, light from the Sun overhead travels relatively shorter distance. At noon, the Sun appears white as only a little of the blue color is scattered whereas, near the horizon, most of the light of shorter wavelength at the blue end of the spectrum are scattered away by the small particles of the atmosphere. Therefore, the light that reaches our eyes is of longer wavelength which gives rise to the reddish appearance of the Sun.

Red light is the least scattered by fine particles, fog or smoke present in the atmosphere which makes it easier to detect it clearly and distinctly to avoid any obstruction.

When a beam of light passes through colloidal solution, it gets scattered causing the light beam to become visible. 

Fine particles scatter light of shorter wavelength and larger particles scatter light of longer wavelength. However, if the size of the scattering particles is large enough, then, the scattered light may even appear white.

The molecules of air and other fine particles in the atmosphere have size smaller than the wavelength of visible light. These are more effective in scattering light of shorter wavelengths at the blue end. This scattered blue light enters our eyes and makes the ocean and sky appear blue.

The molecules of air and other fine particles in the atmosphere have size smaller than the wavelength of visible light. These are more effective in scattering light of shorter wavelengths at the blue end. Whereas, larger particles scatter light of longer wavelengths at the red end.

Violet light scatters the most while red light scatters the least because violet has shorter wavelength and red light has larger.

Scattering occurs when light passes through canopy of dense forests. 

Phenomenon of scattering occurs when light is incident on very small particles and is deflected as a result of it. 

The colour of a colloidal solution depends on the wavelength of the light scattered by the dispersed particles, which in turn depends on the size and the nature of particle.
The colour of water in sea is blue on the scattering of light by water.

Dispersion optical phenomena the splitting of white light into seven constituent colors occur. These colors are often observed as light passes through a triangular prism. Upon passage through the prism, the white light is separated into its component colors - red, orange, yellow, green, blue and violet. The separation of visible light into its different colors is known as dispersion. It was mentioned in the ight and color unit that each color is characteristic of a distinct wave frequency and different frequencies of light waves will bend varying amounts upon passage through a prism. 

After scattering of light by small particles, it spreads in all directions. Hence, the intensity of the scattered light in a direction is smaller then the intensity of the incident light wave.

Tyndall Effect is observed in many natural phenomenon. It involves the scattering of light in a colloidal solution by fine particles. Some common phenomenon include the sunlight entering through forest canopy, sunlight entering a dark room from a small hole and light passed through a milk solution. Speed of light in a medium is defined by the refractive index of the medium. It is maximum for vacuum and is given by the value $3 \times 10^8\ m/s$.

The Tyndall Effect (Tyndall scattering), is light scattering by particles in a colloid or else particles in a very fine suspension. It is observed in aerosol, iris, milk, etc.

The Tyndall Effect (Tyndall scattering), is light scattering by particles in a colloid or else particles in a very fine suspension. The amount of scattering is inversely proportional to the fourth power of wavelength and hence the colour of the colloidal solution is the same as the least coloured wavelength.

After scattering, light is spread in all directions and hence the direction of propagation changes. Wavelength, speed and frequency of the light remains unchanged during the process. Also, the intensity of the light ray in a direction changes.

Scattering is the process of absorption and then re-emission of light energy by particles smaller than the wavelength of the incident light ray. 

In scattering,  light wave is absorbed and re-emitted in all directions without a change in the wavelength of the light ray.

Light of the star is bent  many times and in random directions  as light is bent when it hits a change in density. This random refraction results in the star winking out - twinkling. 

The short-wavelength blue and violet are scattered by molecules in the air much more than other colors of the spectrum because of which blue and violet light reaches our eyes from all directions.

True. This is the reason we can see things around us in Earth's atmosphere.  

The scattering of light depends on the size of the dust particles and the wavelength of the light. The amount of scattering is inversely proportional to the fourth power of wavelength.
Since, violet and blue lights get scattered more than lights of all other colours by the atmosphere the sky appears blue.

During sunrise and sunset the sun rays have to pass through a larger distance and also a greater thickness of air since it is low in the sky. At these positions, the sky looks orange-red colour because photons of red and orange light are least scattered through the atmosphere and are able to reach our eyes.

We see red colour of the sun at sunrise or sunset as the sun at horizon and light rays need to travel a greater distance. In the process of scattering, violet, blue and green rays in the original sunlight are removed and the transmitted beam has yellow and red dominant.

Red light is used as danger signal because it is having high wavelength, less scattering ,hence can travel larger distances.

Blue light is scattered the most. Hence, as sunlight travels the earth, most of the blue colour is scattered and hence spread. This causes the sky to appear blue in the day.

Raman effect is an example of incoherent scattering of light, as it is specific to the molecule which cause it.

Answer is D.

The rainbow is caused by light from the sun (or moon) interacting with raindrops falling from the air. These raindrops are mostly round. A ray of light entering such a droplet is bent (refracted) and decomposed into all possible colors (wavelengths) which the white light consists of. The ray then reflects internally in the droplet, and emerges roughly into the direction it came from when it entered the drop. Since the rays of the different colors all exit at slightly different directions, we see a color band in the sky.
The colors are produced by a phenomenon called dispersion. Dispersion causes white light, which consists of all possible colors to break up into all components, when the light travels from one medium (e.g. air) to another (e.g. water). The different colors of light have all slightly different directions, so if we look in a certain direction in the sky we can see the spectrum.

C. The blue colour of sky is due to scattering of light   = correct statement

The blue colour of sky is due to the scattering of light by small particles of the atmosphere (air molecules) when the light is incident on particles whose size is smaller than the wavelength of light, it is scattered.

According to Rayleigh law, the intensity of scattered light is inversely proportional to the fourth power of wavelength.

Option C is correct answer.

During sunset and sunrise, the rays have to travel a larger part of the atmosphere because they are very close to the horizon. Therefore, light other than red is mostly scattered away. Most of the red light, which is the least scattered, enters our eyes. Hence, the sun appear red..

Answer is A

Setting sun appears to be red because red light which has greatest wavelength is least scattered and reaches our eyes the most. Other wavelength are scattered to the longest extent. So, reason given is wrong.

Larger particles scatter light at the red end of the spectrum the least as the amount of scattering decreases with increase in wavelength..

Colloidal solution of sodium thiosulphate consists of fine particles that mainly scatters blue light. Hence, it appears blue from the side of the beaker.

Particles smaller than the wavelength of light scatters the light in all directions. In visible spectrum, they scatter violet the most and red the least. However, when the particles are larger than the wavelength of light, then the scattering of all wavelengths occur to same extent.

According to Rayleigh's law of scattering, amount of scattering $\alpha \frac {1}{\lambda^4}$.
Red having maximum wavelength straight to the observer.
Most of the scattered light goes towards the sky, so the sky appears blue.

$Scattering$ is the process of absorbed light in all possible directions with different intensities and frequency by an atom or a molecule.