The valency of lead in lead oxide (PbO) is

1. one
2. two
3. three
4. four

two

Reason — The valency of lead in lead oxide can be determined from the formula PbO as below:

$\text{PbO} = \underset{\phantom{1}{1}}{\text{Pb}} \space {\nearrow}\mathllap{\nwarrow} \space \underset{1}{\text{O}} \Rightarrow \overset{\phantom{1}{1}}{\text{Pb}} \space {\nearrow}\mathllap{\nwarrow} \space \overset{1}{\text{O}} \\[0.5em]$

But valency of O is 2. Multiplying by 2, we get:

$\overset{{1 \times 2}}{\text{Pb}} \space {\nearrow}\mathllap{\nwarrow} \space \overset{2 \times 1}{\text{O}} \Rightarrow \overset{\phantom{2}{2}}{\text{Pb}} \space {\nearrow}\mathllap{\nwarrow} \space \overset{2}{\text{O}} \\[0.5em]$

Therefore, valency of Lead is 2.