An unused flashbulb contains magnesium and oxygen. After use, the contents are changed to magnesium oxide but the total mass does not change. This observation can best be explained by the.

this isn't a question, nor is it appropriate for this web site

explanation:

you can't just go around joking about this kind of stuff.

answer:

i havent taken the psat, but i have the sat, make sure to bring some snacks, because youre in there forever, 2 sharp number two pencils, an sat approved calculator, and maybe a jacket.   your phone and any books will be taken up, so don't try to bring them(but they will be given back at the end of the testing).   good luck!   i hope you do well!

answer:

ok i will i'm just bored