Lead.
is the loss of two protons and two neutrons from a nucleus. This decreases the total by ##4## and the by ##2##.
In the form of an equation this is
##””_ 84^218″Po”-> “”_ 82^214″X”+””_ 2^2″He”##
Looking at we can find that element number ##82## is lead, ##”Pb”##, so the product element ##”X”## is ##”Pb”##.