N2^0 -8 2N^+4 /1
O2^0 +4 2O^-2 /2
N2+2O2=>2NO2
Mr ( H2SO3) = 1*2 + 32 + 16*3 = 82
Mr(Ca3(PO4)2) = 40*3 + 31*2 + 16 * 8 = 310
Mr(Cu(OH)2) = 64 + 16*2 + 1*2 = 98