Z is atomic number . Atomic number is the number of protons, atomic number is characteristic for the element.
Protons are positively charged and electrons are negatively charged.
When the number of protons and electrons are equal then the atom is neutral , if there are more electrons than protons then atom is negatively charged and if the atom has more protons than electrons then atom is positively charged .
In this particle there are 25 protons and 23 electrons therefore there are 2 more protons than electrons
The charge of the particle is +2