Question

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

Answer 1

mass number = no. of protons +neutron

39=protons +20

protons = 39-20

=19

atomic number=19

Answer 2

Answer:

The atomic number of an element is 19.

Explanation:

Given

Atomic mass of an atom(Z) =39

Number of neutron(n) =20

To find the atomic number of an element

Solution:

Using the formula of atomic mass

$Atomic mass = number of proton(p) + number of neutron(n)\\39=p+20\\p=19\\Again\\We know\\number of proton=Atomic number of an element\\Atomic number=19$

Hence, the atomic number of an element is 19.