White light comprises of seven colours- Violet, Indigo, Blue. Green, Yellow, Orange , Red. 

Chromatic is something related to color. So "monochromatic" means a single color, which means light of single wavelength. 
Hence correct answer is D.

$Answer:-$ D option

Sir Isaac Newton in 1666 discovered that light consists of seven colours.

Sunlight is reffered as white light.It consist of seven colours,i.e VIBGYOR

Red, blue and green are known as the three primary colours. Those are often regarded as basic colours in nature. By mixing these colours in different proportions, all other colours may be obtained.

Red,blue ,green are known as the three primary colours. By mixing these colours in different proportions, we get all other colours. The primary colours, when mixed in proper proportion, give us white light. Any other colour,produced by mixing two or more primary colours, in different proportions, is called a composite colour.

As violet,indigo,blue,green,yellow,orange and red are the colours of the spectrum.Hence,green is the middle colour in sunlight spectrum.

Isaac Newton was the first person to split sunlight into seven colors using a glass prism. When he tried to split the band of colors further using a second prism placed in the inverted position as compared to that of the first, he observed that the emergent ray was white colored. This gave him an idea that sunlight is made up of 7 colors and any other light that gives a spectrum similar to that of sunlight is often referred to as white light.

The prism splits the incident white light into a band of 7 colors. The various colors seen in the band are arranged in a particular sequence of Violet, Indigo, Blue, Green, Yellow, Orange and Red (VIBGYOR).

When newton's colour disc is rotated at high speed it appears white.

Newton's colour disc, as the name suggests, was invented by Sir Issac Newton and is a disc with seven segments in rainbow colours.
When the disc is rotated, the colours fade to white. In this way, Sir Isaac Newton demonstrated that white light is a combination of the seven different colours found in a rainbow.

Hence, the correct answer is OPTION A.

The sequence of colours obtained on splitting of white light is VIBGYOR- Violet, indigo, blue, green, yellow, orange and red.

Isaac Newton was the first person to split sunlight into seven colors using a glass prism. When he tried to split the band of colors further using a second prism placed in the inverted position as compared to that of the first, he observed that the emergent ray was white colored. This gave him an idea that sunlight is made up of 7 colors and any other light that gives a spectrum similar to that of sunlight is often referred to as white light.

Visible range consists of seven different colours i.e, VIBGYOR. The band of these seven colours is known as spectrum.

Newton's colour disc, as the name suggests, was invented by Sir Issac Newton and is a disc with seven segments in rainbow colours.

Hence, the correct answer is OPTION B. 

Monochrome means single colour. The light of one single colour is monochromatic. White light have seven colours. So it is polychromatic.

Newton's colour disc, as the name suggests, was invented by Sir Issac Newton and is a disc with seven segments in rainbow colours.

Hence, the correct answer is OPTION A. 

As per VIBGYOR we have :Violet, Indigo, Blue, Green, Yellow, Orange and Red colour in rainbow.

Due to persistence of vision the combination of red, green and blue forms the same white color.

Correct answer is (a) Sir Issac Newton.

In 1666, during one of his optical experiments, Newton passed a beam of sunlight through a glass prism. The glass prism split the light into a band of seven colours on his wall. This phenomena is known as dispersion of light

He called this band of colours the ‘spectrum’. Thus the spectrum is a band of seven colours which is obtained by splitting of white light by a glass prism.

The diameter of Newton's rings is inversely proportional to refractive index. Therefore when a drop of water is introduced between the glass plate and plano-convex lens in Newton's rings, the ring system contacts. 

The sun is always behind the observer. This is because the rainbow is actually just sunlight which has been refracted and reflected.

Since diameter of the ring is inversely proportional to the square root of refractive index of the medium between the planoconvex lens and plane glass plate, therefore as refractive index increases, diameter of the rings decrease, that is the rings contract. 

Radius of mth dark fringe   $r _m = \sqrt{mR\lambda}$
Thus we get  $r _{m+4} = \sqrt{7} = \sqrt{(m+4)R\lambda}$     ......(1)
Also,  $r _m = \sqrt{5} = \sqrt{mR\lambda}$      .......(2)
Dividing equation (1) with equation (2),  
$ \sqrt{\dfrac {m+4}{m} }= \sqrt{\dfrac{7}{5}}$
$\dfrac{m+4}{m} = \dfrac{7}{5}$
$5(m+4)= 7m$
$5m+20= 7m$
$2m=20$
$\implies   \ m=10$