Answer:
20 neutrons
Explanation:
In the atom of an element, there exists three subatomic particles namely; proton, neutron and electron etc. The sum of the number of neutrons and number of protons (a.k.a atomic number) in an atom makes up the mass number.
In this question, an element was given as follows: 39- 19 K meaning that the mass number is 39 but the atomic number is 19.
Hence,
no of. neutrons = mass no. - atomic no.
39 - 19 = 20 neutrons.
