1. Calculate the molar mass of NO2:

* N (Nitrogen) has a molar mass of 14.01 g/mol

* O (Oxygen) has a molar mass of 16.00 g/mol

* NO2 has a molar mass of 14.01 g/mol + (2 * 16.00 g/mol) = 46.01 g/mol

2. Convert grams to moles:

* Use the molar mass to convert grams of NO2 to moles:

25.0 g NO2 * (1 mol NO2 / 46.01 g NO2) = 0.543 mol NO2

3. Use Avogadro's number to convert moles to molecules:

* Avogadro's number is 6.022 x 10^23 molecules/mol

* Multiply the number of moles by Avogadro's number:

0.543 mol NO2 * (6.022 x 10^23 molecules/mol) = 3.27 x 10^23 molecules

Therefore, there are approximately 3.27 x 10^23 molecules in 25.0 g of NO2.