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MissPhiladelphia
Avogadro's number represents the number of units in one mole of any substance. This has the value of 6.022 x 10^23 units / mole. This number can be used to convert the number of atoms or molecules into number of moles. We calculate as follows:

 5.05×10^21 atoms Pt ( 1 mol / 6.022 x 10^23 atoms ) (  195.084 g / 1 mol ) = 1.64  g Pt

Answer: 1.6 gram

Explanation:

According to avogadro's law, 1 mole of every substance occupies 22.4 L at STP and contains avogadro's number [tex]6.023\times 10^{23}[/tex] of particles.

To calculate the moles, we use the equation:

[tex]\text{Number of moles}=\frac{\text{Given atoms}}{\text {Avogadro's Number}}[/tex]

[tex]\text{Number of moles of water}=\frac{5.05\times 10^{21}}{6.023\times 10^{23}}=8.4\times 10^{-3}moles[/tex]

1 mole of Platinum [tex]Pt[/tex] weighs 195 g

[tex]8.4\times 10^{-3}moles[/tex]  of Platinum [tex]Pt[/tex] weigh =[tex]\frac{195}{1}\times 8.4\times 10^{-3}=1.6g[/tex]

Thus mass of [tex]5.05\times 10^{21}[/tex] platinum atoms is 1.6 gram.