Determine the molecular formula of the listed compound from its % composition and the molecular mass

C=85.7%
H=14.3
mm =84g/mol

First change the percent to grams and then divide by atomic mass to get moles.
85.7g C/12g C=7.14moles of C
14.3g H/1g H=14.3mole of H
Now divide by the lowest number of moles to get to whole ratios
The emperical formula is CH2
The molecular mass is 84g/mol now divide that by the emperial mass which is 14 ... this equals 6
Distribute the 6 and the answer is C6H12

85.7/12 = 7.14
14.3/1 = 14.3

so CH2 is emprical formula
each CH2 wieghs 12+2 = 14
84/14= 6

C6H12 is molecular formula