Nucleic acids/ nuclein were first discovered by
A. Altmann
B. Fleming
C. Miescher
D. Koch

Hint: Each and every pioneer has significantly contributed to the field of biology. But the scientist who discovered nucleic acid and was able to isolate it was a Swiss physician and biologist.

Complete answer: In option A, Altmann is mentioned. Richard Altmann is responsible for discovering mitochondrion in a cell in the year 1886. He was a German pathologist. As known, mitochondria are considered the powerhouse of the cell because it is the site of ATP or adenosine phosphate synthesis.
In option B, Fleming is mentioned. Alexander Fleming is renowned for his discovery of penicillin. He was a Scottish microbiologist and physician and a Nobel Prize award winner. Penicillin, discovered in 1928 is a group of antibiotics derived from Penicillin moulds and are used to treat many infections.
In option C, Miescher is mentioned. Friedrich Miescher was a Swiss biologist and physician. He was the first one who was able to isolate nucleic acid. He found nucleic acids and was able to demonstrate DNA as a separate molecule. There are two types of nucleic acids presently known. They are RNA and DNA.

In option D, Koch is mentioned. We know that Robert Koch was a German scientist and one of the founders of bacteriology. He is credited for his discovery of the anthrax disease cycle and the bacteria responsible for causing tuberculosis and cholera. He was awarded the Nobel Prize for Physiology or Medicine in 1905 for the same.

Note: The nucleic acids are long chain-like molecules consisting of a series of almost identical building blocks called nucleotides. A nucleotide consists of a pentose sugar, a phosphate group, and a nitrogenous base.