Pb valency in PbO is +2 and in PbO₂ it is +4.

PbO is a basic oxide and simple acid-base reaction takes place between PbO and HNO₃.

On the other hand in PbO₂ lead is in + 4 oxidation state and cannot be oxidised further. Because if see lead’s electronic configuration [Xe] 4f¹⁴5d¹⁰6s²6p², maximum electron lead can give will be four and not more than that because d-orbital is full filled one and thus not letting it donate anymore. Therefore no reaction takes place. Thus, PbO₂ is passive, only PbO reacts with HNO₃.

2PbO + 4HNO₃→ 2Pb (NO₃)₂ + 2H₂O (Acid base reaction)