Deoxyribose glucose guanine phosphate ribose
molecule 1 x x
molecule 2 x x x
molecule 3 x x x
molecule 4 x x

a scientist is purifying dna from a bacterium. during the purification process, a preparation is obtained that contains only four molecules. some components of these molecules are listed in this table. which of the four molecules is the dna?

a) molecule 1

b) molecule 2

c) molecule 3

d) molecule 4

There is no attached table, so it could not be told precisely which of the four molecules is the DNA. But, it is known that DNA consists of deoxyribose, guanine, and phosphate. 
The base unit of DNA is called a nucleotide. The nucleotide consists of a nucleobase (adenine - A, thymine - T, cytosine - C, and guanine -G), a monosaccharide deoxyribose, and a phosphate group. By knowing this, it is easy to choose which molecule of those is the DNA.

Both prokaryotic and eukaryotic cells have ribosomes and cell membranes