The formula for sodium oxide is Na2O. This means that for every 2 moles of sodium (Na), there is 1 mole of oxygen (O).

The molar mass of sodium is 22.99 g/mol, and the molar mass of oxygen is 16 g/mol. So, the molar mass of sodium oxide is:

(2 x 22.99 g/mol) + (1 x 16 g/mol) = 62 g/mol

This means that in 62 g of sodium oxide, there are 32 g of oxygen. So, the percent composition of oxygen in sodium oxide is:

(32 g / 62 g) x 100% = 51.61%