Question

calculate the atomic number of an element whose atomic nucleus has mass number 39 and number of neutron is 20

Answer 1

Atomic number = mass number-number of neutrons so
= 39-20=19 so the atomic number of an element is 19

Answer 2

ANSWER:

                                                          GIVEN,

                                                                   mass number=39

                                                                    nutron number=20

Atomic number=mass number - neutron number

∴Atomic number = 39 - 20                  

                             =19