In		match O-atom with the formal charge.
Column-A		Column-B
$\begin{array}{c}\mathrm{I}\\ \mathrm{O}\end{array}$		-1
$\begin{array}{c}\mathrm{II}\\ \mathrm{O}\end{array}$		0
$\begin{array}{c}\mathrm{III}\\ \mathrm{O}\end{array}$		+1

Formal charge on central atom in ozone is +1 and terminal oxygens are 0 and -1

FC=V-N-$\frac{\mathrm{B}}{2}$  FC =formal charge ,V= no. of valence electrons 

N=No. of non bonding valence electrons, B=total no. of electrons shared in bonds