On the periodic table, there are two numbers in the block for the element potassium, K: 19 and 39.098. What are the names of the numbers and what do they measure?

The names of this numbers are:

atomic mass=A=39.098 (mass of an atom of that element=number of protons+number of neutrons)

atomic number=Z=19=number of protons.

A=Z+N

A=atomic mass

Z=atomic number

N=number of protons.

It represents as 19 K 39.098

Here, upper number which is 19, is atomic number, which means number of protons or number of electrons in non-ion phase.

And, lower number which is 39.098, is mass number, which means the sum of atomic number & number of neutrons ...