1. Find the molar mass of CH4O:

* Carbon (C): 12.01 g/mol

* Hydrogen (H): 1.01 g/mol (x 4)

* Oxygen (O): 16.00 g/mol

Total molar mass of CH4O = 12.01 + (1.01 x 4) + 16.00 = 32.05 g/mol

2. Find the mass of oxygen in CH4O:

* The molar mass of oxygen is 16.00 g/mol.

3. Calculate the percentage of oxygen:

(Mass of oxygen / Molar mass of CH4O) x 100%

(16.00 g/mol / 32.05 g/mol) x 100% = 49.94%

Therefore, CH4O (methanol) is approximately 49.94% oxygen by mass.