Your tool of choice here is Avogadro's constant, which essentially acts as the definition of a mole
$color(blue)(ul(color(black)("1 mole CO"_2 = 6.022 * 10^(23)color(white)(.)"molecules CO"_2))) ->$ Avogadro's constant
So, a mole is essentially a group of things. In this case, a mole of carbon dioxide will contain
You know that
$5.00 * 10^2 color(red)(cancel(color(black)("moles CO"_2))) * (6.022 * 10^(23)color(white)(.)"molecules CO"_2)/(1color(red)(cancel(color(black)("mole CO"_2))))$
$= color(darkgreen)(ul(color(black)(3.01 * 10^(26)color(white)(.)"molecules CO"_2)))$
The answer is rounded to three .