Your answer is

but if you are looking for some explanation check description below :)
Diphosphorus trioxide formula is:

Di stands from 2 atoms of something, in this case we have 2 atoms of Phosphorus.
Trioxide means that we have 3 atoms of oxygen in this substance that's why we have:

And water is just

Unbalanced formula is:

Now we need to balance this equation
On left hand side we have 2 atoms of Phosphorus, on right hand side we have just one atom of Phosphorus, that's why we need to put 2 before

Now we need to count all atoms of oxygen and hydrogen and make it equal on both side.
So we need to put 3 on left hand side before water to make this equation balanced.
That's why correct answer is:
Answer:
an acid is a substance which produces hydrogen ions as the only as the only positive ion when dissolved in water.
Photosynthesis is the process by which plants create their food. It involves the operation of enzymes in the plant cells , and they work best at certainpH levels. ... Thus, as the plant's pH drifts away from the best pH, the rate of photosynthesis will decrease.