Well, calcium carbonate, or limestone, has a chemical formula of #CaCO_3#. It has a molar mass of around #100 \ "g/mol"#.
So, in #10 \ "g"# of calcium carbonate, there will be
#(10color(red)cancelcolor(black)"g")/(100color(red)cancelcolor(black)"g""/mol")=0.1 \ "mol"#
So, there will be #0.1# moles of calcium carbonate in this sample.
One mole of molecules is defined by #6.02*10^23# molecules.
Therefore, there exist #6.02*10^23*0.1=6.02*10^22# molecules of calcium carbonate.
#CaCO_3# consists of one calcium atom, one carbon atom, and three oxygen atoms.
A calcium atom has #20# protons, a carbon atom has #6# protons, and one oxygen atom has #8# protons, and so three oxygen atoms would have #8*3=24# protons.
In total, one molecule of calcium carbonate has #20+6+24=50# protons. But, we have #6.02*10^22# molecules of calcium carbonate.
Therefore, in total, we would have
#6.02*10^22*50=3.01*10^24# protons.
