How many molecules are in3.0 moles of carbon dioxide?

Using the Avogadro Number.

1 mole = 6.022 x 10^(23) atoms/molecules.

Since Carbon Dioxide is a compound molecule (CO2)

Then 3 moles = 3 x 6.022 x 10^(23) molecules.

1.8066 x 10^(24) moleccules.