3. An atom OF
elemente A has mass number 39 and 19 protons
Write the electron arrangement of the atom

Explanation:

Potassium (K) atom has 19 electrons. The full electron configuration of Potassium (K) is 1s22s22p63s23p64s1

the old alchemists made significant contributions to science even though there starting premises were off a bit. their conclusions after failure would steer them into better directions for investigation. science is no more than close observation and the initial mistakes result in rethinking and retrying experiments.