Two atoms with different mass number but the same atomic number are called a) elements. b) ions. c) isotopes. d) nuclei.

What you are describing is a difference in the nucleus of neutrons.

Elements: these chemicals are what is on the periodic table.

ions: These have either too many electrons or too few electrons from the elements found on the periodic table.

Nuclei: are the part of the atom found at the center.

The three above are NOT the answer.

The answer is C

scattering of light by tiny particles in air to produce the colors we see on sky, is dependent on the following factors:

(i) wavelength of light

(ii) size of the scattering particle  

(iii) distance traveled by light through the atmosphere.

according to rayleigh's law of scattering, the amount of scattering is inversely proportional to the fourth power of its wavelength. shorter the wavelength, greater is its scattering. hence violet/blue light is scattered more than red.

sun's light is a composite light ( visible light) with wavelengths in the range 400 nm (violet) to 700 nm (red). as sunlight passes through our atmosphere, the molecules of air scatter light according to their wavelengths. during sunrise and sunset, the sun's position is below the horizon. hence light from the sun travels a greater distance in the atmosphere when compared to its position a noon.

as sunlight enters the earth's atmosphere, blue light is scattered away and at the end of its journey in the sky, only red and orange wavelengths remain in the beam.

hence at sunrise and sunset, the sky appears reddish orange.

i will answer your question if you answer mine