The mass percent of oxygen in CaO is (8 pts)
what is the rest of the choices but I do think it is a
add the reltive atomic mass of Ca and O which are 40 and 16 respectively after addition we get molecular mass of CaO which is 40+16=56now divide atomic mass of O by molecular mass of CaO and multiply it with 100 as show n16/56 *100=28.57%
