What particle is needed to complete this nuclear reaction 222 86 rn }218 84 po?

To complete this reaction a helium particle must be added.

²²²Rn₈₆ --> ²¹⁸Po₈₄ + ⁴He₂

This reaction is an example of α decay. In this decay an unstable atom becomes stable by emitting αparticle that is a nuclei a helium so its mass is reduced by 4 units and its atomic number is reduced by 2 units. And the atom becomes stable .

On going from ²²²Rn₈₆ to ²¹⁸Po₈₄, we can see that there is difference in mass number of 4 and in atomic number of 2. So this is clear that a helium nuclei is emitted.

"among the transition metal elements, manganese and zinc have a slight lowering of electronegativities. the reason behind this is that the nuclear charges of these elements are slightly weaker than the other transition metal elements due to the way their valence electrons are filled up. both manganese and zinc have their valence electrons filled up to the 4th shell with 1 pair of electrons (4s2) completely occupying it. although the electrons in the 3rd shell (3d) are yet to be paired since the outer most shell is filled up, the ability of the nucleus to attract electrons is lessened. hence,   the electronegativity (or the ability to attract electrons) is lessened."

i do not get it   at all