Ratio of number of atoms in one mole of oxygen molecule to ozone is _____.

The correct option is B

$\frac{2}{3}$

Oxygen is diatomic ($O_2$) and ozone is triatomic ($O_3$).

Thus,

1 mole of oxygen = 6.022 $\times$ ${10}^{23}$ molecules of $O_2$ = 2 $\times$ 6.022 $\times$ ${10}^{23}$ atoms of O.

1 mole of ozone = 6.022 $\times$ ${10}^{23}$ molecules of $O_3$ = 3 $\times$ 6.022 $\times$ ${10}^{23}$ atoms of O

The ratio is = $\frac{2\times 6.022\times {10}^{23}}{3\times 6.022\times {10}^{23}}$ = $\frac{2}{3}$