The proportion of number to mol is 1 mol to approximately 6.022 x 10^23, that is, there are 6.022 x 10^23 of somthing in 1 mol of it.
So, using rule of three, we have:
2.8 x 10^23 molecules --- x
6.022 x 10^23 molecules --- 1 mol
[tex]\begin{gathered} \frac{2.8\times10^{23}}{6.022\times10^{23}}=\frac{x}{1mol} \\ x=\frac{2.8\times10^{23}}{6.022\times10^{23}}mol=\frac{2.8}{6.022}\times10^{23-23}mol\approx0.46mol \end{gathered}[/tex]So, this is approximately 0.46 mol or 4.6 x 10^-1 mol.
