The number of valence electrons in the atom is 5 as can be seen from the ionization energy.
Ionization energy is the measure of the readiness of an atom to lose an electron. The lower the value the easier it is for an atom to lose an electron and vice versa.
After the removal of the first electron it becomes increasingly more difficult to remove succeeding electrons because of the imbalance between the positive nuclear charge and the remaining electrons.
Therefore, since we have 5 ionization energies given, the number of valence electrons in this atom is 5.
