Statement-I: The number of atoms in a given mass of dioxygen (oxygen) and trioxygen(ozone) gases is same
Statement-II: The number of atoms depends on atomic mass, not on molecular mass

Let’s take 16grams of each $O_2$ and $O_3$  atoms of

O in  $16{\mathrm{gO}}_2=\left(\frac{16}{32}\right)\times 2{\mathrm{N}}_{\mathrm{A}}={\mathrm{N}}_{\mathrm{A}}$ atoms

Atoms of in 16g  ${\mathrm{O}}_3=\left(\frac{16}{48}\right)\times 3{\mathrm{N}}_{\mathrm{A}}={\mathrm{N}}_{\mathrm{A}}\text{atoms.}$

Hence, 16g of  O, $O_2$  or $O_3$  will contain $N_A$  atoms of O. Statement-II gives explaination of I