How many molecules are there in 79g of Fe2O3? how many atoms is thi

Molar masses:

$m_(Fe) = 56g/mol \\ m_(O) = 16g/mol \\\\ \therefore m_{Fe_(2)O_(3)} = 2 \cdot (56)+3 \cdot (16) = 112+48 = 160g/mol$

So:

$1mol \ Fe_(2)O_(3) = 160g = 6 \cdot 10^(23)molecules$

160g ---------- 6·10²³molecules
79g ---------- x

x = 2.9625·10²³ molecules

1molecule = 5 atoms
2.9625·10²³ molecules = 2.9625·10²³·5 = 14.8125·10²³ atoms