Hi there!
I believe the answer to this is B. Elementary and High school students.
Hope this helps! ☺♥
They depend on nitrogen-fixing bacteria, which convert atmospheric nitrogen into a usable form.
The strong Base with a pH of 12 is reduced by 4 units upon being added with solution Y. If you added a strong acid to the strong base, all ions are present in the solution, yes? So every OH- is neutralised by every H+ for example, meaning the resultant pH should be 7. The resultant pH is only 8 however, so solution Y must be a <em>weak acid </em>only!