Answer
There are $0.0487$ mol, or $2.93 \times 10^{22}$ atoms of platinum in 9.50 g.
Work Step by Step
Atomic weight of platinum (Pt): 195.08; therefore, the molar mass is: $195.08$ $g/mol$
$9.50$ $g$ $\times \frac{1mol}{195.08g} = 0.0487$ $mol$.
Now, find the number of atoms:
$0.0487$ $mol \times \frac{6.022 \times 10^{23}}{1 mol} = 2.93 \times 10^{22}$ atoms.
