He mass number of an atom is equal to the sum of protons and neutrons in the nucleus. A helium atom has 2 protons and 2 neutrons. What is the mass number of this atom?

Mass number= 4

Explanation:

The atom of an element is composed of protons, electrons and neutrons. The number of protons is equal to the number electrons in a neutral atom. The atomic number of an element denoted by symbol Z is the number of protons in the atom of that element while the mass number of an element denoted by symbol A is the sum of the proton number (atomic number) and the neutron number in that element. i.e. A = Z + N where A= Mass no., Z= Atomic/Proton no. , N= Neutron no.

Based on the information above, we can calculate the mass number of Helium element (He), which has 2 protons and 2 neutrons in the nucleus of its atom.

Using A = Z + N

Where A= Mass no

Z = Atomic no = 2

N = Neutron no = 2

A= 2 + 2

A = 4

Therefore, mass number of Helium is 4.