How many atoms are in $2.50$ moles of  $Si{O}_2$ ?

A material, molecule, or atom's number of moles is determined by:

$n=\frac{N}{N_A}$

where N is the number of atoms and $N_A$ is Avogadro's number. The units of the number of moles is the mole or abbreviated mol.

We are given with 2.5 moles of ${\mathrm{SO}}_2$, and we need to find the number of atoms in it. We can clearly see from the formula of ${\mathrm{SO}}_2$ that there is 1 silicon atom and 2 oxygen atoms. Therefore, the total number of atoms in 1 mole of ${\mathrm{SO}}_2$ are $6.022\times {10}^{23}$ molecules/mole $\times 3$atoms/molecule.
As a result we can say that the number of atoms in $2.5$ moles of ${\mathrm{SO}}_2$ will be:

$2.50 \mathrm{mol}\times 6.022\times {10}^{23}$ molecules $/\mathrm{mol}\times 3$ atoms / molecule $=4.52\times {10}^{24}$ atoms.

Hence, option B is correct.