Which of the atoms shown has an atomic number of 4?

Answer: B.
Explanation:
Atomic number of an atom is given by number of protons in the nucleus of the atom.
In a neutral atom, number of electrons = number of protons
option A- atom has 7 protons, thus atomic number is 7
option B- atom has 4 protons, thus atomic number is 4
option C- atom has 3 protons, thus atomic number is 3
Thus, B has atomic number 4. The element Beryllium has atomic number 4