#### Answer

The mass percent composition of sodium in sodium oxide is equal to $74.19\%$

#### Work Step by Step

The formula for sodium oxide is: $2Na^+$ + $O^{2-}$ = $Na_2O$
1. Calculate the molar mass of: $Na_2O$
Molar Mass ($Na_2O$):
22.99* 2 + 16.00* 1 = 61.98g/mol
2. Calculate the total mass of $Na$ in one mole of this compound:
Total Mass ($Na$): $ 2 \times 22.99 = 45.98$
3. Find the mass percent composition:
$\frac{Total-mass (Na)}{Molar-Mass} \times 100\% = \frac{ 45.98}{ 61.98} \times 100\% = 74.19\%$