From the chart;
A - 4
B - 6
C - Be
D - 10
E - 2
F - Ne
The atomic and mass number of atoms
The number of protons in an atom's nucleus determines its atomic number, which establishes an element's identity. The atomic number and the electron count of a neutral atom are likewise equal.
The total of an atom's protons and neutrons is its mass number. It stands for the atom's total mass. Because of differences in the quantity of neutrons, isotopes of the same element have the same atomic number but distinct mass numbers.