A compound contains 4.07% hydrogen, 24.25% carbon and 71.75% chlorine. It's  molar mass is 99.03 g. What is the empirical and molecular formula? 

 Let the total mass of the molecule = 100g
Mass of carbon in the molecule.     =24.25 Mass of hydrogen in the molecule. =4.07 Mass of chlorine in the molecule    =71.75

Number of moles of carbon in molecule = 24.25/12 = 2.02
Number of moles in hydrogen in molecule =4.07/1= 4.07
Number of moles of chlorine in molecule = 71.75/35.5= 2.02

ratio= C:H:Cl= 2.02 : 4.07 : 2.02 = 1:2:1
so empirical formula is CH2Cl
empirical formula mass = 12g + 2g + 35.5g

now N = molecular mass/ empirical formula mass=99.03g/49.5g = 2
molecular formula = N *  empirical formula 
                                  2(CH2Cl)= C2H4Cl2