Answer:
C; 1, 5, 2
Explanation:
First, we do atom inventory:
Think of the arrow as a divider
On the left side, we have 4 phosphorus and 2 oxygens
On the right side, we have 2 phosphorus and 5 oxygens
Now we try to balance:
To make it easier, we want to try and make the 5 oxygens get to an even number so, we put a 2 in front of the P2O5 which makes it 2P2O5
Since we put a 2 in front of the P2O5, we have to multiply our phosphorus and oxygen on the right side by 2, which brings us to now have 4 phosphorus and 10 oxygens.
So now the oxygens are unbalanced.
To balance the oxygens, we put a 2 in front of the O2 located on the left side which makes us multiply our oxygen by 5, making it now 10.
Final result:
We end up having P4 + 5O2 = 2P2O5
(1, 5, 2)