The correct answer is A. PH value
If a substance is very acidity it has a high PH, if it is less acidic (alkalinity) is has a lower PH. For instance, water has a PH of 7 because it is in between of being acidic and alkaline.
The pH unit has 10x as many hydrogens ions as the unit above.
Ex: A pH of 5 would have 10x more hydrogen ions than a pH of 6
and 100x more than if it had a pH of 7.
With a pH of 9 and 3, this is equivalent to 10⁶
So your answer should be:
1,000,000
There are 150 neutrons in 15N
MgH2 + 2 H2O → Mg(OH)2 + 2 H2