2 points If an element has 20 protons, 20 electrons and 20 neutrons, what is the
atomic number of this element?

20

Explanation:

The atomic number of this element is 20.

Atomic number is the number of protons within an atom.

Since we have been given that the number of protons is 20. Therefore, the atomic number is 20.

Mass number of the atom is the number of protons plus the number of neutrons.

For this atom, mass number = 20 + 20  = 40

Atomic number is 20

it should be p1 v1 = p2 v2