Answer: 12.5 moles NaNO3
Explanation: solution attached.
First balance predict the products
Na+ Mg( NO3)2 => Mg + NaNO3
Next balance the chemical equation
2 Na + Mg(NO3)2 => Mg + 2 NaNO3
Solve for the moles of Na
175 g Na x 1 mole Na/ 14 g Na
Next compare the mole ratios of Na and NaNO3 based from the balanced equation.
2 moles Na : 2 moles NaNO3