Answer:
[tex]\boxed{\text{0.17 mol}}[/tex]
Explanation:
[tex]\text{M$_{r}$ of Na} = 22.99\\\text{Moles} = \text{3.9 g } \times \dfrac{\text{1 mol}}{\text{22.99 g}} = \text{0.17 mol}\\\\\text{ The sample contains $\boxed{\textbf{0.17 mol}}$ of Na}[/tex]
