Answer
1.589 g Pt
Work Step by Step
1 mole = $6.022 \times 10^{23}$ atoms
Number of mole = $\frac{atoms}{6.022 \times 10^{23}}$ = $\frac{4.91 \times 10^{21}}{6.022 \times 10^{23}}$ = 0.00815 mole Pt
mass = number of moles $\times$ molar mass
= $(0.00815 mol) \times (195 g/mol)$
= 1.589 g Pt