To convert from particles to moles, you need to divide by Avogadro's constant.
To convert from moles to grams, you need to use the molar mass.
1.2*10^22 particles * (1 mole/ 6.022*10^23 particles) * (106 grams/1 mole) = 2.1 g Na₂CO₃
Remember, our final answer will have 2 significant digits because it is limited by the 2 sig figs in 1.2*10^22.
There are 2.1 grams of sodium carbonate in 1.2*10^22 particles of sodium carbonate.