An atom has 12 protons, 11 neutrons and 12 electrons. What is the mass member of this atom?

the mass is 24

Explanation:

The atomic number is defined as the totall number of electons in the atom in its non bonded state.

Thus the number of electron is 1w, atomic number is also 12.

Mass number is defined as the number of protons + neutrons in the nucleus of an atom.

atomic mass = 39

number of neutrons = 20

number of protons= 19

electronic configuration = 1s2 2s2 2p6 3s2 3p6 4s1

the number of electron in first shell = 2

number of electrons in n=3 shell = 8