The Formula to find the number of moles is:
Number of Moles = Mass/ Molar Mass
Which means that Mass = Number of Moles * Molar Mass
We know that Number of Moles of Sodium Na = [tex]1.5*10^_{-3}[/tex] moles
If you check the Periodic Table, Molar Mass of Sodium Na = 23g/mol
So, Mass = [tex]1.5*10^_{-3} * 23[/tex] = [tex]3.45 * 10^{-2}[/tex]
So, the mass in grams of [tex]1.5*10^_{-3}[/tex] mol of Sodium is [tex]3.45 * 10^{-2}[/tex]
Hope this Helps :)