Answer:
12 more oxygen
Step-by-step explanation:
An atom is the smallest particles that can take part in a chemical reaction
The given compounds are:
3Mg₃(PO₄)₂
Number of oxygen atoms = 3[2 x 4] = 24 oxygen atoms
For;
4Al₂O₃;
Number of oxygen atoms = 4 x 3 = 12 oxygen atoms
In 3Mg₃(PO₄)₂ , there are 24 - 12 = 12 more oxygen atoms than in 4Al₂O₃;