Answer:
1.34x10^-3 moles.
Explanation:
To convert from atoms to moles, you'd need to multiply the value of atoms by a number called the Avogadro's Constant, used in converting moles 6.023x10^23, to get the moles.
8.13x10^20 divided by 6.023x10^23=0.0013498
Since the significant figures tell us to use three digits (in case of multiplication or division, use the smallest number of sig figs involved), so we should do 1.34x10^-3 moles.
