A specific element's atomic mass is the weight of one of its atoms. The atomic mass is measured in unified atomic mass units, which are denoted by the letter "u". The combined mass of all the protons, neutrons, and electrons in an atom is its atomic mass.

When compared to the mass of a proton or neutron, the mass of an electron is extremely small. Consequently, you may say that the atomic mass is the sum of the masses of all the protons and neutrons that make up an atom's nucleus.
We know that the nucleus of an atom, which solely includes protons and neutrons, is where the majority of the stuff in an atom is concentrated since many tests conducted for atomic models have shown this to be the case.

The number of protons and neutrons in an atom are simply added to determine the atomic mass of that particular atom. Consider an oxygen atom, for instance, which has 8 electrons, 8 protons, and 8 neutrons. You just need to double the atomic mass of oxygen by 8 protons and 8 neutrons.
Therefore, oxygen has an atomic mass of 8+8=16.
The periodic chart also includes the atomic mass of each element. The atomic mass is expressed in decimal numbers and atomic mass units in the periodic table.

Hence, option B is correct.