divide the percentages by the relative atomic mass of the elements
C:- 70.58 / 12 = 5.882
N:- 11.76 / 14.006 = 0.84
H:- 4.23 / 1.008 = 4.2
O:- 13.43 / 15.999 = 0.84
so the ratios of the elements C:N:H;O = 5.882/0.84 : 1 :4.2/0.84 : 1
C = 7 , N = 1 H = 5 and O = 1
answer is C7H5NO
