Răspuns:
72 g apa = 0.072 kg
Mai intai aflam numarul de moli de apa:
n = masa/masa molara = 0.072 / 18 = 0.004 moli
intr-un mol de apa................Na molecule
in 0.004 moli de apa....................x
x=0.004 * Na molecule = 0.004 * 6.022 * 10²³ molecule
