Firstly, we know that M= m/n, the main formula which shows the relationship between m, n, and M. The nknown compound contains only carbon, hydrogen, and oxygen, so we can get n(C)=m/M, from M(C)= m(C)/n (C), besides the stoechiometric equality, we have n( C)= m(C)/M(C ) = m(CO2)/ M(CO2)=11/44, because m(CO2)=11.0, M(CO2)=44.01 so n(C )= 0.24moles,