How many moles of carbon dioxide molecules
are there in 50g of carbon dioxide?

3.011×1023 individual carbon dioxide molecules

C. exhaust gases flowing from a car's tailpipe

Explanation:

As gases have a submicroscopic particle all of which are rapid and constant in motion.  There properties such as pressure-temperature and viscosity by considering there molecular composition and motion is thus the greatest kinetic energy.  The collision of particles thus is fastest in these when blowing through an exhaust in a car's tailpipe.