At sunset the sun appears reddish what is most likely the reason for this phenomenon

Scattering of light is responsible for the red appearance of the sun at sunset and sunshine. Sunlight have seven colors which is denoted by VIBGYOR in which violet is having the least wavelength and red is having the highest wavelength.

During sunshine and sunset, the sun is close to the horizon as a result sunlight has to travel more distance to the atmosphere so most of the colors are scattered in the atmosphere due to their shorter wavelength but red light due to the highest wavelength does not scatter much.

As a result, the only red light of the sun reaches our eyes which generates the red appearance of the sun at sunset and sunshine.

explanation:

b,bacteria convert nitrates

into nitrogen gas.

d,plants and animals take in

and use nitrogen compounds.

e,bacteria break down waste    

products and return nitrogen  

to the soil.

a,bacteria convert atmospheric

nitrogen to ammonia.

c,bacteria convert ammonia

to nitrites and nitrates.

it would lead to upper respiratory infections and pneumonia.