The question requires us to identify the atomic mass of potassium, as shown in the periodic table.
The periodic table of elements, as shown below, shows basic information on all chemical elements. The atomic mass is usually shown on the top of the element symbol:
We can identify the element potassium (K) on the first column and fourth line of the table. The number that appears above the symbol "K" refers to its atomic mass. We can see in the table that the atomic mass of potassium is 19 (letter D).