Whenever Pb shows inert pair effect it always form:

Explanation

The inert pair effect is the effect of the s-orbitals in which they do not participate to make bonds with other molecules because the electrons are held tightly due to the strong attraction of the nucleus towards the electrons. The reason for this effect is that the elements having the f-orbital show poor shielding effect due to their diffused shapes. As a result, the nuclear charge on their s orbitals increases due to this poor shielding effect. This results in more attraction and binding of the electrons in the s-orbitals which stops them from getting out and prevents the metal to acquire a +4 oxidation state. The electronic configuration of lead isPb (82) = (Xe) 4f14 5d10 6s2 6p2Due to the inert pair effect, the +2 oxidation state of Pb is more stable than its +4 oxidation state. Further on moving down the group, the ionization enthalpy decreases. As a result, the sum of the first two ionization enthalpies of Pb is quite low and hence Pb can easily lose two electrons to form Pb2+ ions. Consequently, Pb forms ionic compounds.