120 grams of NaOH means 3 Moles of NaOH because 40 grams (Molecular Weight in grams) is one mole of NaOH.
Each mole of any substance contain Avogadro’s number of molecules ie., 6.022 x (10 to the power 23).
Hence 3 Moles of NaOH contain 3 times of Avogadro’s number of molecules ie., 3 x 6.022 x (10 to the power 23)
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: A
Explanation: the only way to turn it from blue to yellow is to mix it with an acidic solution.
Answer:
Nuclear fission
Explanation:
Because the little particles are being spread out and the two elements are broken apart