moles = mass/molar mass
Mass of Na given = 28 grams
Molar mass of Na = 22.989 grams/mol
So, 28 grams of Na = 28/22.989 = 1.218 moles Na ≈ 1.2 moles Na
Since the mass was given to two significant digits, the number of moles is approximated to two significant digits as well, that is, about 1.2 moles.
