First, we need to find the number of moles of platinum in 5.23x1021 atoms. We can do this by dividing the number of atoms by Avogadro's number, which is 6.022x1023 atoms/mol:
$$moles \ of \ Pt = \frac{5.23\times10^{21} \ atoms}{6.022\times10^{23} \ atoms/mol} = 8.68\times10^{-3} \ mol$$
Now, we can use the molar mass of platinum to calculate the mass of 5.23x1021 platinum atoms by multiplying the number of moles by the molar mass:
$$mass \ of \ Pt = 8.68\times10^{-3} \ mol \times 195.084 \ g/mol = 1.70 \ g$$
Therefore, the mass of 5.23x1021 platinum atoms is 1.70 grams.
