Atoms can have different numbers of which of the following electrons, protons neutrons or all of the above

Atoms may have different numbers of neutrons. Atoms are the smallest fraction of an element that can exist, and still show the properties of the element. They consists of electrons (negatively charged), protons (positively charged), and neutrons (no charge). The number of electrons is equivalent to the number of protons normally however an atom may loose or pick up electrons and  have a positive charge or negative charge. The number of neutrons in the nucleus may vary within a given element to give varieties of atoms we call isotopes. 

The basic repeating unit of nucleic acids are known as nucleotides. a nucleotide consists of three distinct chemical groups.