Witch of the following is not a purine?

Guanine

Cytosine

Thymine

none of the above

Cytosine and thymine.

Explanation:

DNA is present as genetic material in all the living organism except some viruses. The structure of DNA contains a nitrogenous base, a pentose deoxyribose sugar and a phosphate group.

The nitrogenous base of DNA are characterized into purines and pyrimidines. The pyrimidines are six member ring and contains thymine and cytosine. Purines are nine member rings and contain adenine and guanine.

Thus, the correct answer is option (2) and (3).

Cytosine and thymine

Explanation:

Purines - Adenine, guanine

Pyrimidines - cyosine, thymine, uracil (in RNA)