1. Avogadro's Number

Avogadro's number tells us that there are 6.022 x 10²³ particles (atoms, molecules, etc.) in one mole of any substance.

2. Calculation

* Start with the number of moles: 4.91 moles of nitrogen trifluoride (NF₃)

* Multiply by Avogadro's number: 4.91 moles * (6.022 x 10²³ molecules/mole)

* Calculate: 2.96 x 10²⁴ molecules of NF₃

Answer: There are approximately 2.96 x 10²⁴ molecules of nitrogen trifluoride in 4.91 moles.