Respuesta :

1. 60% (There are 5 elements and 3 are oxygen; 3/5=60%)

2. 40% (There are 5 elements and 2 are iron; 2/5=40%)

3. 40% (There are 5 elements once you distribute the 2 and it becomes MgO2H2, 2 are oxygen, 2/5=40%)

Hope this helps!