Answer
$5.39\times10^{21}\ atoms\ Bi $
Work Step by Step
1.Use the molar mass of bismuth and Avogadro's number as conversion factors in order to determine the number of atoms of bismuth.
2. $1.87 g\ Bi \times\frac{1\ mol\ P}{208.9804\ g\ Bi}\times\frac{6.022\times10^{23}}{1\ mol\ Bi}= 5.39\times10^{21}\ atoms\ Bi $
