* Hydrogen's Oxidation Number: Hydrogen typically has an oxidation number of +1, except when it is bonded to a metal, in which case it has an oxidation number of -1.

* Overall Charge: PbH4 is a neutral molecule, meaning its overall charge is zero.

Let's set up the equation:

* Let 'x' be the oxidation number of Pb.

* We have 4 hydrogen atoms, each with an oxidation number of -1.

Therefore, the equation is: x + 4(-1) = 0

Solving for x:

* x - 4 = 0

* x = +4

The oxidation number of Pb in PbH4 is +4.