Respuesta :

Answer:

40%

Explanation:

We'll begin by obtaining the molar mass of MgO. This is illustrated below:

Molar Mass of MgO = 24 + 16 = 40g/mol

Observing the formula MgO, we have 1 atom of O in it.

The percentage composition by mass of oxygen in MgO is given by:

Mass of O/Molar Mass of MgO x 100

= 16/40 x 100 = 40%