4. How many molecules are equal to 2.25 moles of sulfur dioxide?

We know that one mole of any chemical compound always contains 6.022 x 10^23 molecules. Therefore, we can calculate the number of molecules of 2.25 moles of sulfur dioxide SO2 by multiplying the number of moles by the Avogadro's constant 6.022 x 10^23:

2.25 moles SO2 (6.022x10^23 molecules/1mole) = 1.355 x 10^24 molecules of sulfur dioxide