Question

What is the change in oxidation number of Pb during conversion of $PbO_2$ to $Pb(NO_3)_2$ ?

• A. +2 to +4
• B. +4 to +2
• C. +4 to +7
• D. +4 to +6

Answer 1

Answer: (B)

+4 to +2

Answer 2

For $PbO_2$:

Let oxidation state of Pb = $x$. With oxygen at $-2$,

$$x + 2(-2) = 0 \implies x = +4.$$

For $Pb(NO_3)_2$:

Since $NO_3^-$ has a charge of $-1$, and there are 2 nitrate ions,

$$x + 2(-1) = 0 \implies x = +2.$$

Thus, the oxidation number of Pb changes from $+4$ to $+2$.