**Oxidation Number of Lead in Litharge**

Litharge is an inorganic compound with the chemical formula PbO. It is a yellowish or reddish-brown solid and is commonly known as lead(II) oxide. The oxidation number, also known as the oxidation state, is a concept used in chemistry to represent the charge an atom would have if all the bonding electrons were completely transferred to the more electronegative atom.

**Determining the Oxidation Number of Lead in Litharge**

To determine the oxidation number of lead in litharge, we need to consider the following rules:

1. The oxidation number of an atom in its elemental form is always zero. Since lead is in the compound litharge (PbO), it is not in its elemental form and does not follow this rule.

2. The oxidation number of oxygen in most compounds is -2. In the compound litharge (PbO), there is only one oxygen atom, so its total oxidation number contribution is -2.

3. The sum of the oxidation numbers in a compound must equal zero. In the compound litharge (PbO), the sum of the oxidation numbers must equal zero.

**Using the Rules to Determine the Oxidation Number**

We can use the rules mentioned above to determine the oxidation number of lead in litharge:

1. Let's assume the oxidation number of lead in litharge is x.

2. The oxidation number of oxygen is -2, and there is one oxygen atom in litharge. Therefore, the total oxidation number contribution of oxygen is -2.

3. The sum of the oxidation numbers must equal zero. So, the equation becomes: x + (-2) = 0.

4. Solving the equation, we find that x = +2.

Therefore, the oxidation number of lead in litharge is +2.

**Explanation of the Result**

The oxidation number of +2 indicates that lead has lost two electrons and has a positive charge of +2 in the compound litharge. This means that lead is in the +2 oxidation state in litharge. The oxidation number of +2 is also consistent with the fact that litharge is known as lead(II) oxide.

In conclusion, the oxidation number of lead in litharge is +2.