To find the number of moles of a compound given its mass, we can use the Molar Mass of that compound.
In this case, we have 15.0 g of krypton, which is an atom, so we can consult its molar mass from a periodic table.
Consulting it, we get:
[tex]M_{Kr}=83.798g/mol[/tex]The molar mass, the mass and the atomic number are related by the following:
[tex]\begin{gathered} M_{Kr}=\frac{m_{Kr}}{n_{Kr}} \\ n_{Kr}=\frac{m_{Kr}}{M_{Kr}} \end{gathered}[/tex]Substituting the values we have:
[tex]n_{Kr}=\frac{15.0g}{83.798g/mol}\approx0.179mol[/tex]Thus, there is approximately 0.179 mol in 15.0 g of krypton.
