Scantrons use #2 pencils, but which #2 should i use the 2H or the 2B one?
It does not matter, so long as the pencil doesn’t rip the sheet.
The US #2 pencil is equivalent to an HB. An HB or a 1B would be a better choice than 2B (very soft and hard to erase well if you want to change an answer), and much better than a 2H which might take too long to fill in the blanks.