An atom of potassium has an atomic mass of 39 amu and an atomic number of 19. it therefore has neutrons in its nucleus.
a. 19
b. 39
c. 20
d. 2
select the best answer from the choices provided
a
b
c
d

C. 20 because 39-19 is 20 so there are 20 neutrons and the atomic number is the same as number of protons and electrons.

Six amino acids have side chains that are polar but not charged. these are serine (ser), threonine (thr), cysteine (cys), asparagine (asn), glutamine (gln), and tyrosine (tyr). these amino acids are usually found at the surface of proteins, as discussed in the proteins 2 module.