The formal charges on the three oxygen atoms in ${\mathrm{O}}_3$ molecule are

 According to the electron-dot structure, there are 12 number of bonding electrons and 6 number of non-bonding electrons.
Now we have to calculate the formal charges of each oxygen atom.
 

$$\begin{gathered} \mathrm{Formal} \mathrm{charge}= \\ \mathrm{Valence} \mathrm{electrons}-\mathrm{Non}-\mathrm{bonding} \mathrm{electrons}-\frac{ \mathrm{Bondingelectrons} }{2} \\ \mathrm{Formalcharge} \mathrm{on} {\mathrm{O}}_1=6-2-\frac{6}{2}=+1 \\ \mathrm{Formal} \mathrm{charge} \mathrm{on} {\mathrm{O}}_2=6-4-\frac{4}{2}=0 \\ \mathrm{Formal} \mathrm{charge} \mathrm{on} {\mathrm{O}}_3=6-6-\frac{2}{2}=-1 \end{gathered}$$

Hence, the correct option is (D).