C. How many molecules are in 0.400 moles of N205?

2.408x10^23 molecules

Explanation:

Avogadro's hypothesis gives us a background understanding that 1mole of any substance contains 6.02x10^23 molecules.

From the above conclusion,

1mole of N205 contains 6.02x10^23 molecules.

Therefore, 0.4mole of N2O5 will contain = 0.4 x 6.02x10^23 = 2.408x10^23 molecules

nacl or sodium chloride is an ionic compound. this is because an ionic compound pertains to a compound that consists of positively and negatively charged ions. in this case, na (sodium) has a tendency to lose one electron when it reacts with with other atoms, so the resulting sodium ion contains 11 protons and 10 electrons, thus making it positively charged (na+), when chlorine reacts, it usually gains one electron to form an ion called chloride, thus making it negatively charged ( since the ions are oppositely charged, they attract.