Answer
$1.7g\ Na$
Work Step by Step
Divide the compound by its molar mass to get the number of moles of the compound. Multiply by the ratio of moles of the compound to moles of sodium to get the number of moles of sodium. Multiply by the molar mass of sodium ($22.99\frac{g}{mol}$) to get the mass of sodium.
$8.5g\ Na_{2}C_{6}H_{6}O_{7}\times\frac{1mol\ Na_{2}C_{6}H_{6}O_{7}}{236.087g\ Na_{2}C_{6}H_{6}O_{7}}\times\frac{2mol\ Na}{1mol\ Na_{2}C_{6}H_{6}O_{7}}\times\frac{22.99g\ Na}{1mol\ Na}= 1.7g\ Na$
