<span>An
atom with an atomic number of 12 has 12 protons. Because the mass
number is the sum of the protons and neutrons, the mass number would
need to be at least 12. I hope this helped!
</span>
X: Ozone layer destruction
Y: Mass extinction
By universe expanding
by galaxies looking redder than they should be
capturing the afterglow of the big bang
how starlight differs from microwaves
peeking back in time