Final answer:
To find the number of moles in 1.9 x 10^25 formula units of NaCl, divide the number of units by Avogadro's number, which gives approximately 3.2 moles. The correct answer is A. 3.2 moles.
Step-by-step explanation:
To determine how many moles are in 1.9 x 1025 formula units of NaCl, we can use Avogadro's number, which is 6.022 x 1023 formula units per mole. This is the most important conversion factor in chemistry for converting between particles and moles. So, the calculation would look as follows:
Number of moles = (Number of formula units) / (Avogadro's number)
Number of moles = 1.9 x 1025 / 6.022 x 1023
This gives us approximately 3.2 moles of NaCl. Therefore, the correct answer is A. 3.2 moles.