m ( P 2 O 5) = 0.210 g
M ( P 2 O 5 ) = 2 * 30 + 5 * 16 ( from the Periodic Table ) =
= 60 + 80 = 140 g/mol
N = m / M = 0.210 g/ 140 g/mol = 0.0015 mol
Avogadro Constant: N a = 6.02 * 10^23
n = N * N a = 0.0015 * 6.02 * 10^23 =
= 0.00903 * 10^23 = 9.03 * 10^20 atoms
